Automatic blood smear device
United States Patent [1 1 Levine et al.  
 [Ill 3,880,111  
 1 Apr. 29, 1975 1 1 AUTOMATIC BLOOD SMEAR DEVICE [75] Inventors: Marshall S. Levine. Wayne; Albert A. Faulkner. Conshohocken, both of Pa.  
 [731 Assignee: Geometric Data Corporation, Wayne, Pa.  
 [22] Filed: Nov. 5, 1973 2n Appl. No.: 413.004  
 Primary Examiner- Mervin Stein Assistant Exammar-Douglas Salscr Artur-net, Agem, or Firm-Ceasar. Rivise. Bernstein &amp; Cohen [57] ABSTRACT A blood smear device which automatically prepares a slide for a blood cell analysis is shown The device includes holding means for supporting a slide, spreading means provided in contact with the slide and translation means for causing relative movement between the slide and the spreading means. A drop of blood is placed on the top surface of the slide at one end thereof and the spreading means is located adjacent the other end of the slide prior to preparation of the slide. Control means are provided for causing the translation means to cause relative movement of the spreading means towards the drop of blood until the spreader means contacts the drop The control means includes delay means for preventing further movement of the spreader means relative to the drop for a predetermined period of time The control means causes the spreading means to be moved relatively away from the drop after the predetermined period of time. The control means continues the movement until the spreading means is disposed in its original position with respect to the slide.  
 40 Claims. 16 Drawing Figures PATENTEDAPRZQ I975 SHEET 2 0F 4 FIG. //76 45a /02 /5.9 F/G. 6  
 AUTOMATIC BLOOD SMEAR DEVICE This invention relates generally to blood analysis and more particularly to a device which automatically makes blood smears on glass slides for the purpose of blood cell analysis.  
  In order to analyze blood and specifically to make a white blood cell differential count, it is necessary to have a slide prepared with a specimen of blood smeared on the slide. The blood smear must be so made that a monolayer of blood is formed so that the cells can be examined under a microscope by a technician. The technician then counts the number of different types of white cells that are present in the sample in order to provide a white blood cell differential count. The most commonly used method of preparing a blood smear on a slide is the glass slide technique. This utilizes two 3 X l glass slides. A drop of blood is placed on a first slide and the second slide is used to smear the blood along the first slide. A Wright Stain is then applied to the blood smear in order to facilitate differentiation of the white cells from the red cells.  
  The problems with the manual techniques used are that there is a lack of uniformity in the appearance of the smear, even when the same person has prepared all of the slides. There is great difficulty in preparing the slide because the slides are difficult to hold, the angle between the first and second slide is critical, as well as the speed of the movement of one slide with respect to the other.  
  It has been estimated that over 50 percent of blood smears made in institutions are not good. A bad slide causes a skewed distribution of the white blood cells which therefore makes it difficult to provide accurate blood cell counts since the choosing of the wrong area of the slide to examine will cause a distortion of the count. Moreover, the pressure provided from one slide to the other in making the smear is also critical. If the pressure between the slides is released at the end of the smear, then the monolayer which is critical to examination of the smear will be lost.  
  With the advent of automatic blood cell differential analyzers, the need for a blood smearing device which provides uniform smears has become critical. That is. unless there is a uniform area of monolayer in the smear which is large enough, automatic blood cell differential analyzers do not adequately provide a good white blood cell differential count.  
  There have been various attempts at making devices which will make it possible to provide uniform slides. Such devices are shown in the following patents:  
 PATENTEE PATENT NO. ISSUE DATE W. Schiller l.858,3(l8 May l7, I932 Chapin et al 3,470,847 October 7, I969 Grabhorn 3,633,850 August l5. I972 439,124 (German) January 4, l927 ers of blood on a slide. However, there are problems with devices of the centrifuge type in that they cause distortion of red cells. The smear provided on the slide is often too thick or too thin based on the hematacrit of the blood. Moreover, platelets tend to clump together instead of being evenly distributed which makes it difficult to estimate the population of platelets to white blood cells and red blood cells. Moreover, there is a potential health hazard from the centrifuge type blood smearing devices in that the device uses a spinning portion in which the blood is distributed. Because of the vaporization of blood into the atmosphere. the atmosphere can easily become contaminated.  
  Finally, one of the greatest disadvantages of the centrifuge type of smearing device is that there is a large requirement of blood in comparison to the techniques previously discussed. For example, in a presently existing device of the centrifuge type, there is the requirement of thirty to fifty microliters of blood in order to make a smear. Thus, the finger-stick technique for drawing blood is not adequate for supplying blood to a centrifuge type of blood smearing device. in the finger stick technique, blood is taken from the finger by pricking the finger with a needle and then placing the droplet directly on the slide. The centrifuge type of blood requirement also makes it very difficult to use in pediatrics where infants have too little blood to spare for such a technique.  
  It is therefore an object of this invention to overcome the aforementioned disadvantages of prior blood smearing devices.  
  Another object of the invention is to provide a new and improved blood smearing device which enables the making of uniform slides irrespective of the operator of the device.  
  Another object of the invention is to provide a new and improved blood smearing device which provides a blood smear with a large monolayer area for analysis in white blood cell differential counts.  
  Still another object of the invention is to provide a new and improved blood smearing device which provides uniform slides for analysis by an automatic blood cell differential analyzer.  
  Yet another object of the invention is to provide a new and improved automatic blood smearing device which automatically optimizes the critical functions in the creation of a uniform blood smear having a large monolayer area.  
  These and other objects of the invention are achieved by providing a blood smearing device for preparing a slide for a blood cell analysis. The slide has a drop of blood on the top surface and located towards one end of the slide. The device includes holding means for supporting the slide and spreading means provided in contact with the slide. Translation means are also provided for causing relative movement between the slide and the spreading means. The spreading means is located adjacent the other end of the slide prior to preparation of the slide. Control means are provided for causing the translation means to cause relative movement of the spreading means towards the drop of blood until the spreading means contacts the drop. The control means includes delay means for preventing further movement of the spreading device relative to the drop for a predetermined period of time. The control means initiates the translation means after the period of time to cause the spreading means to be moved relatively away from the drop. The control means causes the movement until the spreading means is disposed in its original position with respect to the slide.  
  Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
  FIG. I is a perspective view of a blood smearing device embodying the invention;  
 FIG. 2 is a top plan view of the device;  
  FIG. 3 is an enlarged perspective view of the slide smearing area with the slide holder in a retracted position;  
  FIG. 4 is an enlarged top plan view of the blood smearing device embodying the invention with the cover portion removed;  
  FIG. 5 is a sectional view taken along the line 5-5 in FIG. 4;  
  FIG. 6 is an enlarged sectional view taken along the line 66 in FIG. 4;  
  FIG. 7 is an enlarged exploded view of the slide holder assembly;  
  FIG. 8 is an enlarged fragmentary sectional view with portions shown in full for purposes of clarity taken within the area 8 in FIG. 5;  
  FIG. 9 is an enlarged sectional view taken along the lines 9-9 in FIG. 8&#39;,  
  FIG. 10 is an enlarged side elevational view of the spreader in contact with the slide;  
 FIG. 11 is a top plan view ofa blood smear on a slide;  
  FIG. 12 is a schematic electrical diagram of the control circuitry utilized to operate the device for a blood smear;  
  FIG. 13 is a top plan view of an alternate slide holder embodying the invention;  
  FIG. 14 is a fragmentary sectional view taken along the line I4-I4 in FIG. 13;  
  FIG. I5 is an enlarged fragmentary sectional view similar to the view taken along line 14-14 in FIG. 13 of a second alternate slide holder embodying the invention; and  
  FIG. 16 is a front elevational view of an alternate spreader in contact with a slide with the slide holder shown fragmentarily and the slide shown in vertical section.  
  Referring now in greater detail to the various figures of the drawings wherein like reference numerals refer to like parts, the blood smearing device of the present invention is generally shown at 20 in FIG. 1. Blood smear device 20 basically comprises a housing 22, a slide holder 24, a pair of spreading device holders 26 and 28 and a pair of glass slides 30. The housing 22 has mounted in the front surface thereof a switch 32 which connects and disconnects the power and a control knob 34 which can be utilized to adjust the thickness of the smear. Also mounted in the front portion of the housing are a pair of buttons 36 and 38 for initiating a smearing cycle. Either one of the buttons 36 or 38 may be pressed. The buttons 36 and 38 are placed on the left and right sides of the device, respectively, to enable either a left-handed or right-handed operator of the device to have equal facility in initiating operation of the blood smearing device.  
  The slide holder 24 and spreading device holders 26 and 28 are mounted within a U-shaped track 40 which acts to guide the movement of the slide holder 24.  
  In operation, one or a pair of slides 30 is provided on the slide holder 24. A drop of blood is then placed on a predetermined position of each of the slides 30 determined by the location of an indicating spot (shown in phantom in FIG. I) under each of the slides. The button 36 or 38 is pressed which thereby causes the slide holder to be retracted within the housing as shown in FIG. 3. When the spreading means contacts the drop of blood on each of the slides 30, the slide holder is slowed and a suitable delay is caused before the holder 24 is moved out of the housing. The delay period provides an adequate period of time for the blood to spread across the edge of the spreading means. When the delay period is over. the movement of the slide holder 24 towards its initial position causes a smearing of the blood on slides 30.  
  The construction of smearing device 20 is best seen with respect to FIGS. 4, 5 and 6.  
  The translation means for moving the spreading means with respect to the blood on the slide 30 is best seen in FIG. 4. The translation means includes a motor 42 which is connected via a suitable gear train (not shown) to drive shaft 44. The drive gear of shaft 44 which is connected to the gear train is shown at 46 in FIG. 5. Shaft 44 is journaled in and supported by bracket assembly 48 which suitably houses the gear train. Connected to the top of the shaft 44 is a drive arm 50 which is connected to the top of shaft 44 and is fixedly connected thereto so that it rotates with shaft 44 about the longitudinal axis of shaft 44. Also connected to shaft 44 is a cam 52 which is spaced from the arm 50 by a collar 54 which is mounted about shaft 44. Cam 52 is also fixedly secured to the shaft 44 so that it rotates with shaft 44. Also mounted on bracket 48 is a microswitch 56. In addition, associated circuitry including a transformer 58, a powerline 60 and fuse 62 are mounted adjacent bracket 48 as seen in FIG. 4.  
  As best seen in FIG. 5, the drive arm 50 is connected to the slide holder 24 via a linking member 64. Linking member 64 is connected at its first end to the drive arm 50 by a threaded fastener 66. The fastener 66 extends through a slotted opening 68. The threaded member 66 includes a suitable boss adjacent the head thereof so that the screw 66 is slidable in slot 68 while providing a secure fastening to the drive arm 50. An opening is provided at the other end of linking member 64 through which a threaded fastener 70 extends to connect the linking member to the slide holder 24. The slide holder 24 includes a recess 72 in which the end of the linking member is fastened so that the head of the threaded fastener 70 will be below the top surface of the slide holder 24. The linking member 64 includes two metal strips which are spaced by and connected together by a vibration isolating member 74. Member 74 is preferably comprised of a material such as nylon or neoprene rubber which acts to isolate the vibrations from the motor which are transmitted via the shaft 40 from the slide holder 24. It should be understood, however, that the member 74 is of a high tensile strength so that linking member 64 acts as a rigid member.  
  The vibration isolating member 74 includes a pair of slots in which the end pieces 76 and 78 of the linking member 64 are received and are then suitably secured to the vibration isolating member by suitable fasteners 79. End piece 76 of the linking member 64 includes a central angled portion so that the force from the drive arm 50 can be transmitted to the level of the slide holder 24. The linking member 64 is pivotable about the threaded fastener 70 and is pivotable around and slidable about the threaded fastener 66 to enable the rotational movement of drive arm 50 to enable a linear motion of the slide holder 24 which is guided by track 40.  
  As is best seen in FIG. 7, the slide holder 24 includes a pair of recesses 80 and 82 in which the slides 30 are held in place with respect to the slide holder 24. At the rear of each of the recesses 80 and 82 a leaf spring 84 is mounted. As best seen in FIG. 8, leaf spring 84 is substantially S-shaped and is embedded and secured in the bottom surface of recess 80 and extends slightly above the upper edge or top surface of the slide 30. The slides 30 are slid into contact with the leaf spring 84 and the front edge of the slide is lowered into the recess and the spring 84 acts to press the slide 30 against the forwardmost edge of the recess 80 within the holder 24.  
  Referring back to FIG. 7, it can be seen that beneath the front edge of the recesses 80 and 82 of the slide holder 24 a pair of semi-cylindrical notches 86 are provided. The notches 86 enable a finger to be placed underneath the slide 30 when disposed in recesses 80 and 82 to remove the same from the slide holder 24.  
  Also provided on each of the recesses 80 and 82 are spot indicators 88 which can be seen through the glass slide when disposed in the recesses so that a drop of blood may be placed directly over the spot 88. As seen in FIG. 7, on slides 30 a drop of blood 90 is provided on each of the slides which is aligned with the spot 88 in recesses 80 and 82.  
  The size of the spots 88 also enables the operator to place a preferred amount of blood on the slide. That is, the preferred amount of blood exactly covers the spot 88. The size of the spot thereby acts as a guide to the amount of blood required for a blood smear.  
  The slide holder 24 is translatable in track 40 which includes a pair of cars or projections 92 which are planar and extend upwardly from the upstanding legs of the track 40. Each of the projections 92 includes an opening 94 in which is mounted a shaft 96 which pivotably supports the spreader holders 26 and 28 (see FIGS. 5 and 6). Provided in the base wall of track 40 is a pair of openings 98 which are provided on opposite sides of an extended slot opening 100. As best seen in FIG. 5 and FIG. 6, the track 40 is supported by and connected to a pair of brackets 102 via suitable fasteners I04 which extend through openings 98 in the track 40.  
  As is also best seen in FIG. 7, a nylon sheet 106 is provided between the track 40 and the slide holder 24. The sheet 106 is connected to the bottom of slide holder 24 and is held against the base of track 40 by assembly I08. Assembly 108 includes a nylon sheet 110, a metal plate 112, a leaf spring 114, and a metal plate I16. The nylon sheet 110, the metal plate 112, the leaf spring I14 and the metal plate 116 each have a pair of openings which are aligned with respect to each of these items and through which a pair of threaded fasteners I18 extend. The fasteners 118 are threaded at their uppermost end and extend through a pair of openings in nylon sheet 106 and are engaged in a pair of openings in slide holder 24. A nylon washer 120 is provided about each of the fasteners between the nylon sheets I06 and 110 which fit within the slot 100 of track 40. The washers prevent the sheets I06 and I from being urged into slot I00 about the fasteners H8.  
 The leaf spring II4 acts to provide uniform pressure from sheets 106 and 110 against the top and bottom surfaces of the track 40 so that the slide carrier 24 slides smoothly along track 40. The slotted opening acts to guide the linear movement of slide holder 24 in track 40. Also, the nylon sheets I06 and which move with the slide holder 24 act to reduce friction between the slide holder 24 and track 40.  
  The spreader holders 26 and 28 are each similarly constructed and are supported by shaft 96 as best seen in FIGS. 5 and 6.  
  Each of the spreader holders 26 and 28 include a pair of pinch members 122 and I24. Pinch member 122 is the planar end portion which extends at an angle from the main portion of an elongated planar lever member 126. Lever member 126 includes an integral depending member I28 having a cylindrical end I30. Pinch member 124 is integrally connected to the spreader holding member 132 of the holders I26 and 128 and extends parallel to pinch member I22. The member 132 in cludes a recess which includes a cylindrical surface therein in the uppermost surface of the member 132 which receives the cylindrical end 130 of lever member 126 and journals the lever member therein. The cylin drical surface extends over an arc of more than 1 80 to maintain said cylindrical end therein. Additionally. at the rear of member I32 a recess with a cylindrical surface therein is provided which receives shaft 96 and enables the member 132 to rotate about shaft 96. The cylindrical surface which journals shaft 96 also extends over an arc of more than 180 to maintain said shaft therein. The cylindrical portion of the surface about shaft 96 is slightly larger in diameter so that there can be a slight rocking about the horizontal axis extending from front to rear of each of the holders 26 and 28. As will hereinafter be seen, this enables the necessary tilting of the spreaders to cause self alignment of the spreaders with the top surfaces of the slides.  
  A vertically extending opening is also provided in member 132 through which a pin 134 extends. The pin extends through the entire member 132 from top to bottom and extends out the bottom surface of member 132. As best seen in FIG. 8, a leaf spring 136 is secured to member 132 by a threaded fastener 138. The fastener I38 maintains the leaf spring against pin 134 which is urged against the bottom surface of the lever member 126. As seen in FIG. 5, provided adjacent the transversely extending member 128 of lever member 126, on the opposite side of member 128 from the pin 134, is a pad 140 which is preferably made of a cushioning material such as polyurethane foam and which is adhesively secured between the lever member 126 and the member 132.  
  The spreader holding member 132 of each of the holders 26 and 28 also includes a slot in the forwardmost end of the member 132 which receives a spreader 142. As best seen in FIG. 8, the spreader 142 has a chamfered lowermost edge 144. The spring 136 maintains the spreader 142 within the slot in member 132 by pressing against the under surface 146 of the spreader. thereby pinching the spreader between the spring I36 and flange 147 of member I32. The flange 147 extends parallel to the spreader I42 and extends outwardly from the member 132.  
  In order to remove or insert a spreader. the pinch members 122 and I24 are engaged by the fingers manually and squeezed together. This causes pin 134 to be pushed downwardly, as seen in FIG. 8, against the spring 136 thereby urging spring 136 away from surface 146 of spreader 142. This enables removal or insertion of a spreader in the holding member 132.  
  As best seen in FIG. 8 and FIG. 9. each of the holding members 132 include a pair of depending projections 148. The projections 148 are provided on each side of the holding members 132 of each of the spreading device holders I26 and 128. Projections I48 coact with a pair of projections 149 which extend upwardly from the top surface of the slide holder 24. The projections 149 are suitably formed by the rounded heads of threaded fasteners which are threadedly secured to the slide holder 24. Each of the projections 149 are aligned with one of the projections 148 of each of the holders 26 and 28 to enable the spreaders to be lifted above the slides 30 when the slide holder 24 is moved to the outermost position of the blood smearing device 20. This enables the spreader 142 to clear the leaf spring 84 as well as to enable the spreader to be smoothly set down upon the glass slide when the slide holder 24 is moved inwardly of the blood smearing device.  
  As is best seen in FIG. 6, the buttons 36 and 38 are mounted in openings 150 of the housing 22. Each of the buttons 36 and 38 are connected to pins 152 which depend therebeneath. The pins are mounted in the opening of a rectangular bridging section 154 of a bracket 156. Each of the bridging sections 154 include an opening in which the pin 152 is slidable vertically. An elongated bar 159 extends between the brackets I56 and is mounted beneath each of the rectangular bridging sections 154 and is urged thereagainst by coil springs 158. The lowermost edge of coil springs I58 are suitably secured to the base of the housing. The bar 159 has mounted thereon a microswiteh 160 which is mounted adjacent the assembly 108 which rides with the slide holder 24. At each end of the bar 159 is provided a U-shaped slot 162 which receives the legs of brackets 156 to prevent the bar 159 from moving away from bracket I56. The arm of the microswiteh 160 is engaged by the assembly 108 when the slide holder 24 is in the outermost position shown in FIG. 5.  
  The spreader 142 is preferably made of glass. The wettability of glass is important because it enables the drop of blood to spread quickly and be spread optimally as the spreader moves with respect to the slide. As best seen in FIG. 10, the chamfered edge of the spreader 142 rests on the top surface of the slide 30. The rockability of the holding member with respect to shaft 96 assures that there is alignment of and substantial contact along the entire surface of the chamfered edge of spreader 142 with the top surface of the slide 30. The spreader 142 is so positioned with respect to the slide that the facing surface 170 of spreader 142 is at approximately a 35 angle with respect to the horizontal top surface of the slide 30.  
  When the face surface 170 contacts the spot of blood 90, the blood 90, because of the wettability of the glass spreader 142, starts to spread from the center towards the edges of the spreader 142. After the blood has had an opportunity to spread adjacent the side edges of the spreader 142, the spreader 142 is moved in the direction of arrow 172 as shown in FIG. l and thereby causes the blood to be smeared across the top surface of the slide 30 and thereby form a blood smear basically as shown in FIG. 11.  
  The blood drop as shown in FIG. 11 was originally at the position shown at 174. The portion of the smear shown in shading at 176 represents the excess portion of the blood which is not used for a blood cell differential count. The unshaded portion 178 of the blood smear represents the feathered edge or monolayer within which the blood cells can be analyzed. Thus, in order to cause the blood smear shown in FIG. 11, it is necessary that the spreader 142 be moved in a first direction with respect to the drop of blood to be brought in contact with the drop of blood 90, a sufficient dwell time be allowed to enable the blood 90 to spread towards the lateral edges of the spreader I42 and then the spreader be moved away in the reverse direction at a continuous and predetermined speed.  
  It should be noted that the spreader 142 is wider than a slide 30 so that the lateral edges of the spreader 142 overhangs a slide 30. The overhang prevents the surface edges of the spreader 142 which normally makes contact with the slide from being chipped or scratched when a slide is not placed in one of the recesses 80. The overhanging portion of the spreader slides along the top surface of the holder 24 with the portion of the spreader in the center aligned over recess 80.  
  The control circuitry to enable the smearing cycle is shown in FIG. 12. Basically, the control circuitry of the smearing device includes a motor 42, a microswiteh 56, a microswiteh and a pair of variable resistors I80 and 182. The transformer 58 shown in FIG. 4 converts the power provided via power cord 60 from 1 15 volts A.C. to a lower voltage which is rectified and provides positive voltage on line 184 and ground at line 186. The power line I60 is connected to the transformer 58 in FIG. 4 via the fuse 62 and the ON-OFF switch 32 in a conventional manner. The source of voltage provided on lines 184 and 186 to the circuitry in FIG. 12 is provided from the outputs of the rectifier connected to the transformer 58.  
  Line 186 is connected to the motor 42 via line 188 and via line 190 to an input line of the switch 160. The second input line 192 of microswiteh 160 is connected to the input of microswiteh 56. Microswitch 56 also has lines 194 and 196 connected thereto. Line I94 is connected to one end of variable resistor 182 and line 196 is connected to one end of resistor I80. The other end of resistors I80 and 182 are connected together to line 184 and connected to +V. In order to further illustrate the operation of the control circuitry, the slide holder 24 is schematically illustrated adjacent microswiteh 160. Also, the depending projection 108 represents the assembly 108 at the bottom of the holder 24. The mi croswitch 160 is shown supported by bar 159 which rests on springs 158 and is movable downwardly by either the button 36 or 38 when either is depressed. Adjacent the microswiteh 56 is cam 52 which is similarly associated with the microswiteh 56 as seen in FIG. 4. The microswiteh 56 includes an arm 198 which is contactable by portion 200 of the cam surface of cam 52. Microswitch 160 includes an arm 202 which is contactable by assembly 108 which depends below the slide carrier 24.  
  In addition to the previously set forth input lines to microswiteh 160, microswiteh 160 is also connected via line 204 to motor 42. The microswitches S6 and 160 operate similarly. That is. microswiteh 56 includes an NO and NC legend adjacent lines 194 and 196. When the arm 198 is not contacted. line 192 is connected to line 196 but disconnected from line 194. When arm 198 is abutted by surface 200 of cam 52, then line 192 is connected to line 194 and disconnected from line 196. Similarly, when projection 108 does not contact arm 202 of microswitch 160, the line 204 is connected to line 192 and disconnected from line 190. When the projection 108 contacts arm 202, line 204 is connected to line 190 and disconnected from line 192.  
  The operation of the control circuitry shown in FIG. 12 is as follows:  
  In the initial position of the slide holder 24 as shown in FIG. 1 in its outwardmost position with respect to the blood smearing device. the assembly 108 below slide holder 24 is in contact with arm 202 of microswitch 160. After a drop of blood 90 is placed on the slides 30, the button 36 or 38 is depressed thereby lowering the bar 159 and thereby causing the microswitch 160 to be moved away from the assembly 108 and thereby causing arm 202 to be released to its normal position which causes line 204 to be connected to line 192 within the microswitch 160. The connection of line 204 to line 202 within microswitch 160 causes the conduction between ground and +V across motor 42 via resistor 180, microswitch 56, line 192 to line 204 and to one side of motor 42 and via line 188 to motor 42.  
  As soon as motor 42 is energized, the slide holder 24 is moved away from its initial position and starts moving inwardly of the blood smearing device as indicated in FIG. 3. When the button 36 or 38 is released, even though microswitch 160 returns to its normal position, the assembly 108 does not contact arm 202 and thereby enables the continuation of the energization of motor 42. The movement of the slide holder 24 is caused by the rotation of arm 50 in a counter-clockwise motion as shown in FIG, 4. When the arm 50 is moved approximately 180 the cam 52 has been rotated to a point where the cam surface 200 contacts arm 198 and thereby causes the energization of the motor 42 to be via resistor 182.  
  The resistor 182 has a high impedence and thereby causes an immediate slow down of the rotation of shaft 44 and thus the speed of rotation of arm 50 which rotates therewith. The slowing of the movement of the arm 50 in combination with the slot 68 then causes a dwell time of at least one second at which time the slide carrier 24 is at its innermost position with respect to the device. At this time, the facing surface 170 of spreader 142 is in contact with the blood spot 90 on both slides 30. That is, the indicating spots 88 of the slide carrier 24 is moved to a position directly below the face surface 170 of each of the spreaders 142. Thus, the drops of blood which have been aligned with the indicating spots 88 on the top surface of the slide make contact with the face surface of spreaders 142.  
  For approximately 90 of movement of the arm 50 the cam surface 200 of cam 52 contacts arm 198 of microswitch 56 and thereby continues the lower speed of movement of the shaft 44 and arm 50 in a counterclockwise direction. The slot 68 also enables the slide holder 24 to be stationary with respect to the spreader holders 26. As soon as cam surface 200 leaves the arm 198 the microswitch 56 causes conduction between line 192 and line 196 through the smaller resistor 180 thereby causing the speed of movement of arm 50 in a counter-clockwise direction to increase and substantially simultaneously the threaded fastener 66 connected to arm 50 contacts the forwardmost end of slot 68 and thereby urges the linking member to push the slide holder 24 which causes a swift movement of slide holder 24 to its original position outwardly of the blood smearing device to the position shown in FIG. 1.  
  As soon as the slide holder 24 has reached its original position, the assembly 108 contacts arm 202 of microswitch thereby causing the motor 42 to be deenergized as a result of line 204 being disconnected from line 192 in microswitch 160.  
  It should also be noted that the contacting of arm 202 by assembly 108 also causes line 204 to be connected to line 190 thereby providing a circuit through the motor 42 which further acts to shunt the motor and provides a braking action which causes a very quick stop of the motor.  
  Each of the slides 30 will then have a blood smear similar to that shown in FIG. 11 provided thereon.  
  The slides 30 may then be removed by placement of one finger in notch 86 and then lifting the slide out of the recess of holder 24. New slides are then inserted and drops of blood placed on the slides in alignment with indicating spots 88 and then pressing either button 36 or 38 initiates the next smear cycle.  
  It should also be noted that the glass spreaders 142 are removable and replaceable. In order to remove the spreaders 142, the holders 26 and 28 may be pivoted upwardly holder 28 is shown in FIG. 1. The pinch members 122 and 124 may then be squeezed towards each other manually and the spreader 142 removed and replaced by a similar spreader.  
  The provision ofa thick glass spreader has several advantages. One of the advantages is that the face surface is wide enough that it will not allow the blood spot 90 to spill over the top of the face surface 170, unless too large a drop of blood 90 is placed over the indication spot 88. Secondly, a thicker spreader 132 is more durable and is less subject to cracking and breakage. The chamfered surface 144 on the spreader 142 also enhances durability as well as making it more difficult for the drop of blood 90 to creep underneath the lowermost surface of the spreader 142 which is in contact with the top surface of the slide 30. Moreover, the length of the face surface of the thicker spreader enables the spreader to face outwardly of the blood smearing device which facilitates holding for replacement and insertion of new spreaders, as well as cleaning of the spreader surface when needed.  
  Advantages also accrue from the spreader holder construction which not only facilitates the replacement of spreaders 142, but also includes a rockability about shaft 96 to further cause alignment between the lowermost surface of the spreader 142 with the top surface of glass 30. Thus, a uniform pressure is provided along the entire length of the edge of spreader 142 which is in contact with the top surface of the slide 30. The pivotability of the holders 26 and 28 about shaft 96 also enables the weight of the holder to provide the entire pressure between the spreader 142 and the slide 30.  
  The depending projections 148 of the holders 26 and 28 combined with the upstanding projections 149 on the slide holder 24 assure that the spreader is lifted off of the glass as the slide holder returns to its normal position as shown in FIG. 1. That is, as best seen in FIG. 8, as slide holder 24 moves to the left in FIG. 8 when it returns to its normal position, there is a lifting of the spreaders 142 as projections 149 abut projections 148 thereby lifting spreaders 142 so that their lowermost edges clear the leaf springs 84. This movement of the spreaders 142 with respect to slide 30, as the spreader and slide move with respect to each other, is indicated by arrows 204 in FIG. 8.  
  Similarly, when the slide holder 24 is moved to the right. as shown in FIG. 8, the projection 148 is enabled to be lowered when the upstanding projection 149 clears the rightmost edge of the projection and thereby enables the spreader 142 to be lowered onto the slide 30 after the spreader 142 has cleared the spring 84.  
  It can therefore be seen that a new and improved blood smear device has been provided. The slide holder 24 has two recesses and two spreaders are provided so that a pair of blood smears can be prepared simultaneously with the blood smearing device.  
  The leaf spring 84 in each of the recesses enables the slide to be snapped into the recesses into fixed securement. The springs 84 further enable the slides to be fixed with respect to the recess even when the slides vary slightly in length. If the slide is movable in the recess it can produce a poor smear. The springs obviate this problem.  
  Moreover, the entire smearing operation is made automatic from the time that the blood drop is placed on the indicating spots and the cycle initiated by the pressing of button 36 or button 38. This provides not only uniformity of blood smears, but also excellent blood smears in view of the fact that the dwell time is optimized so that the exact amount of spreading of a blood drop across the face of the spreader is accomplished each time a blood smear is made.  
  Moreover, the adjustable resistances enable optimum smear speed to be accomplished which is also critical to the thickness of and uniformity of the smear. The knob 34 is utilized to adjust the resistance of resistor 180 which controls the exact speed of the smearing portion of the blood smear cycle. The resistors 182 can be adjusted to provide the predetermined amount of time which is required for the face surface 170 of the spreader to be in contact with the blood to enable the blood to spread laterally along the surface 170 of the spreader.  
  Having once determined the resistance required to maintain the face 170 of the spreader in contact with the blood drop 90 for a period of one to three seconds, which has been found to be the optimum dwell time, the resistor 182 need have no further adjustment and the blood smears produced will be of uniform and high quality, The varying of the resistance in the smear resistor 180 by turning of knob 34 enables the operator of the device to obtain either thick, medium or thin densities of smear depending on the requirement of the device.  
  As set forth above. the controlling of the dwell time can be used for varying the width of the smear. By providing a narrower smear, the distribution of cells within the blood smear is varied and this is often desirable. Accordingly, the dwell time can be controlled by resistor 182 to provide a shorter dwell time to provide narrower blood smears It should be noted that the glass spreaders 142 are wider than the slides 30. This enables the Spreaders 142 to have an overhanging portion which extends beyond the width of the slide. The overhanging portion of the spreader contacts the strips surrounding the recesses for slide 30 when a slide is not in the recess and prevents contact of the spreader edge 144 against the lowermost surface of the recesses if a slide is not placed in one or both of the recesses of the slide holder. Accordingly, only the overhanging edge of the spreader I42 contacts the top surface of the slide holder surrounding the recesses so that the face surface 170 and the edge 144 are not scratched or cracked by contact against the base surface of the recesses 80.  
  The uniformity and quality of the blood smear are further enhanced by the maintaining of the same angle between the face surface 170 and the top surface of the slide at all times from the time that the drop of blood is contacted until the last cell is smeared onto the top of the surface. The disposal of the spreader in such a position with the face surface 170 with respect to the top surface is at 30 and also enhances the quality of the smear.  
  It should also be noted that the angle between the face surface of the slide also controls the speed at which the drop of blood spreads on the face surface of the spreader when the spreader contacts the blood. By reducing the angle, the speed of spreading is increased. Accordingly, it is contemplated that in order to obviate the need for changes of speed in the translation means a movable holder for the spreader may be provided in order to change the angle of the spreader with respect to the slide as the spreader is moved with respect to the slide.  
  As is set forth above, the spring 84 in each of the recesses of the slide holder 24 are provided to assure that the outermost edge of the slide is urged against the outermost wall of the recesses of the slide holder 24. The reason is that the movement of the slides within the recesses as the spreader moves along the slide could prevent the face surface of the spreader 142 from contacting the drop of blood originally placed over the indicating spot 88. That is, if the slide could move in the recesses the drop of blood will have been moved out of alignment with the spot thereby preventing the spreader from reaching the drop of blood.  
  An alternate slide holder embodying the invention is shown in FIGS. 13 and 14. The slide holder 224 is similar to slide holder 24 in that it includes recessed area 72 for securement to the linking member 64 which connects the holder 224 to the translation means. in addition, the slide holder 224 also includes semi-cylindrical notches 86 to enable removal of slides 30.  
  However, the recesses 280 for the slides 30 have been modified in that the lowermost or base surface 282 of each of the recesses 280 lies in a plane which is at a small angle with respect to the horizontally disposed top surface 284 of the holder 224. The plane of surface 282 thus extends downwardly from its uppermost point at the rearmost edge 286 of recess 280 to its lowermost point at the front edge 288 of the recess 280. As best seen in FIG. 14, a pair of wedges 290 are provided in the forwardmost corners of each of the recesses 280 adjacent edge 288. Wedges 290 are preferably comprised of a compressible resilient material such as an epoxy resin or rubber. The slide 30 is thus placed in each of the recesses by pressing the innermost edge of slide 30 against the rearmost vertical surface of edge 286 of the recess and then resting the forwardmost edge of the slide 30 on the pair of wedges 290.  
  The wedges 290, because they are compressible, prevent movement of the slide 30 within the recess 282 since the forwardmost edge of the slide 30 is wedged into the compressable wedges 290. Thus, the slide 30 remains stationary when the spreader member is moved across the top surface of the slide 30.  
  Moreover, the wedge 290 accomodates slight variations in the length of slide 30. When the slides 30 are of the average length. the slides 30 are substantially horizontally disposed since the forwardmost lower edge of slides 30 rests on a level substantially on the same level as the rearmost lower edge of slide 30. Slight variations in the size of slide 30 do not cause large changes in the angular disposition of the slide as a result of the small angle of the wedges 290. The wedges 290 are preferably secured to the forwardmost corners of the recesses 282 by a suitable adhesive.  
  A second alternate embodiment of a slide holder embodying the invention is shown in FIG. 15. Slide holder 324 shown therein is substantially identical to slide holder 224 with the exception that the wedges 290 are replaced by a pair of step platforms 390 in each of the recesses 280. The step platforms 390 are suitably secured in each of the forwardmost corners of the recess 280 and include a stepped slide supporting surface 392. The depth and height of the steps are small so that when slide 30 is placed into recess 280 the amount of movement of the slide 30 as a spreader is passed over the topmost surface of the slide 30 is reduced considerably. Accordingly, each of the steps act as a shoulder to prevent movement of the slide 30 with respect to the slide holder when a spreader is moved along the top surface of a slide.  
  As set forth above. the width of the blood smear controls the distribution of cells in a blood smear. An alternate spreader embodying the invention is shown generally at 442 in FIG. 16. The spreader 442 includes a face surface 470 and an uppermost edge which is chamfered similarly to spreader 142. The spreader 442 is interchangable with spreader I42 in the spreader holders 26 and 28. The outermost edge of the spreader 442 is discontinuous as a result of a pair of semi-circular notches 472 which :ause a central face surface 470 to be formed which is spaced from overhanging end surfaces or edges 474 which are coplanar with surface 470.  
  As can be seen in FIG. 16, surface 470 is narrower than the width of slide 30 which enables a drop of blood to spread only along the length of surface 470 even if the dwell time that the face surface 470 is in contact with a drop of blood is longer than that required for a drop of blood to reach the lateral extents of surface 470. Accordingly. by suitable placement of notches 472. the width of the blood smear can be limited to an exact width. Also. the overhanging edges 474 act to prevent the surface 470 from contacting the base surface of the recess for slide 30 when a slide 30 is not placed in one of the recesses of the slide holder 24.  
  Without further elaboration, the foregoing will so fully illustrate our invention that others may. by applying current or future knowledge. readily adapt the same for use under various conditions of service.  
 What is claimed as the invention is:  
  l. A smearing device for slides. said device enabling a drop of fluid to be placed on the top surface of said slide and located towards one end thereof, said device including holding means for supporting a slide. spreading means provided in contact with said slide, translation means for causing relative movement between said slide and said spreading means. said spreading means being located adjacent the other end of said slide prior to smearing said slide. control means for causing said translation means to cause relative movement of said spreading means towards said one end until said spreading means reaches the position for said fluid. said control means including delay means for maintaining said spreading means for a predetermined period of time at said position for said fluid, said control means initiating said translation means after said period of time to cause said spreading means to be moved relatively away from said position, said control means causing said movement until said spreading means is disposed in its original position with respect to said slide.  
  2. The smearing device of claim I wherein said spreading means comprises a basically rectangular spreader and said surface for contacting said fluid is the outermost edge of said spreader.  
  3. The smearing device of claim 1 wherein said spreading means comprises a glass spreader. said spreader including a chamfered lowermost edge, said chamfered edge being in contact with said top surface of said slide.  
  4. The smearing device of claim 1 and further including spreader holding means. said spreader holding means including self aligning means for causing uniform pressure along the edge of said slide in contact with said spreading means.  
  5. The smearing device of claim 4 wherein said self aligning means comprises an opening in said spreader holding means. a shaft extending to said holding means, said opening being journalled about said shaft and being larger in diameter than said shaft to enable said holding means to rock with respect to said shaft to enable the lowermost edge of said spreading means to be aligned with the top surface of said slide.  
  6. The smearing device of claim 1 wherein said spreading means includes spreader holding means and a spreader with said spreader holding means including a slot for receiving said spreader and resilient means for abutting said spreader to maintain said spreader in said slot.  
  7. The smearing device of claim 6 wherein said spreader holding means includes means for urging said resilient means away from said spreader to enable replacement of said spreading means.  
  8. The smearing device of claim 7 wherein said spreader holding means includes a holding member. said holding member having an outwardly extending member, said means for urging said resilient member including a second outwardly extending member. said resilient member being urged away from said spreader holding means when said outwardly extending members are squeezed together.  
  9. The smearing device of claim 8 wherein said holding member includes an opening which extends through said holding member. said means for urging said resilient member including a lever member which is pivotably secured to said holding member and a pin. said resilient member comprising a leaf spring which is secured to said holding member. said pin extending between said lever member and said leaf spring.  
  10.. The smearing device of claim 6 wherein said spreader holding means is pivotably mounted to a supporting device. said pivotable connection enabling the weight of said spreader and said spreader holding means to maintain said spreader against said slide for smearing said fluid.  
  11. The smearing device of claim 6 wherein said spreader holding means pivots upwardly to facilitate replacement of said spreader.  
  12. The smearing device of claim 1 wherein said slide supporting means includes a recess for receiving said slide and means for limiting movement of said slide in said recess.  
  13. The smearing device of claim 12 wherein said means for limiting movement comprises a spring memher for securing said slide between said spring member and one edge of said recess.  
  14. The smearing device of claim 12 wherein said re cess includes a base surface which is inclined at a slight angle from rear to front, said recess including support ing means at the front of said recess which engages the front edge of said slide to limit movement.  
  15. The smearing device of claim 14 wherein said means at the front includes at least one wedge of resilient material, said slide being engaged by said wedge to limit movement of said slide.  
  [6. The smearing device of claim 14 wherein said supporting means includes a stepped platform, said slide resting on one of the steps of said platform whereby movement of said slide in said recess is limited.  
  l7. The smearing device of claim 1 wherein said translation means moves said means for supporting said slide.  
  18. The smearing device of claim 17 wherein said means for supporting a slide supports a pair of slides and a pair of said spreading means are provided so that a pair of slides are prepared simultaneously.  
  19. The smearing device of claim I wherein said fluid is blood and said smearing device prepares said slide for blood cell analysis.  
  20. The blood smear device of claim 1 wherein said translation means includes a motor, a shaft rotated by said motor, an arm rotated by said shaft and a linking member for connecting said arm to said slide supporting member.  
  21. The smearing device of claim 20 wherein said control means includes means for controlling the speed of translation of said slide supporting member.  
  22. The smearing device of claim 2] wherein said linking member includes lost motion means comprised of a slot in said linking member to enable said arm to be rotated for a portion of the translation cycle without moving said slide with respect to said spreader.  
  23. The smearing device of claim 22 wherein said slide supporting means is guided by track means to move linearly in response to actuation by said rotating arm and said linking arm.  
  24. The smearing device of claim 1 wherein said control means includes means for controlling said prede termined time that said spreading device is maintained at said position for said fluid, said time being predetermined in accordance with the width of the smear desired.  
  25. The smearing device of claim 24 wherein said predetermined time is controlled by means for controlling the speed of said translation means.  
  26. The smearing device of claim 2 wherein said surface for contacting said fluid is narrower than said slide so that said smear is limited in width to the width of said surface for contacting said fluid.  
  27. The smearing device of claim 26 wherein said spreader includes a pair of notches in the outermost edge thereof, said notches being provided one at each end of said surface for contacting said fluid.  
  28. A blood smear device for preparing a slide for a blood cell analysis. said slide having a drop of blood on the top surface and located toward one end thereof. said device including holding means for supporting a slide, spreading means provided in contact with said slide, translation means for causing relative movement between said slide and said spreading means, said spreading means being located adjacent the other end of said slide prior to preparation of said slide. control means for causing said translation means to cause relative movement of said spreading means towards said drop of blood until said spreading means contacts said drop, said control means including delay means for maintaining said spreading means in contact with said drop for a predetermined period of time, said control means initiating said translation means after said period of time to cause said spreading means to be moved relatively away from said drop, said control means causing said movement until said spreading means is disposed in its original position with respect to said slide.  
  29. The blood smearing device of claim 28 wherein said translation means causes movement of said slide holding means for causing relative movement between said slide and said spreading means.  
  30. The blood smearing device of claim 29 wherein said control means includes means responsive to the location of said slide holding means for varying the speed of movement of said slide holding means.  
  31. The blood smearing device of claim 30 wherein said means responsive includes a first switching device which is abutted by said slide holding means for terminating movement of said slide holding means.  
  32. The blood smearing device of claim 31 wherein said control means includes a second switching device which is abutted by said translation means when said wiping means contacts said drop. said contacting of said second switching device causing said translation means to be moved at a second speed during said predetermined period of time, said second speed determining the length of said predetermined period.  
  33. The blood smearing device of claim 32 wherein said control means includes means for varying said sec ond speed so that said predetermined period can be varied for controlling the width of said blood smear.  
  34. The blood smearing device of claim 32 wherein said translation means includes lost motion means which enables said translation means to be moved without movement of said slide holding means during said predetermined period.  
  35. The blood smearing device of claim 34 wherein said device further includes a member for moving said first switching device away from said slide holding means to enable said control means to initiate said translation means.  
  36. The blood smearing device of claim 28 and further including indicating means for indicating the location that a drop of blood should be placed on the top surface of said slide.  
  37. The blood smearing device of claim 36 wherein said indicating means comprises a spot located in said slide holding means underneath said slide. the size of said spot determining the size of said drop of blood placed on said slide for said blood smear.  
  38. The blood smearing device of claim 28 wherein said slide holding means includes means for maintain- 18 said spreading means comprises a generally rectangular spreader and a holder for said spreader, said holder being pivotably supported by said blood smearing device and being upwardly pivotable to replace said spreader and downwardly pivotable to cause said spreader to contact said slide.