the syringe of the present invention , a preferred embodiment of which is illustrated in fig1 includes a body 10 having a barrel portion 1 which outwardly is generally configured as a right circular cylinder for most of its length and has a frusto - conical portion 2 near the distal end , where the body diameter reduces down to the diameter of a conventional hub 3 , upon which is mounted ( preferably detachably ) a conventional hollow needle 4 . the body 10 includes a hollow bore ( shown in phantom ) which is open at the proximal end to receive a plunger member 20 . the bore within the barrel portion of the syringe body is generally configured , according to convention , as a right circular cylinder so dimensioned that the plunger shaft 23 , with the piston 21 at its distal end , fits closely but slidably therein . the syringe body 10 is preferably made of moldable plastic in a single piece , but any of a number of other materials would also be suitable , including for example glass or metal , and the body could be made in multiple pieces which could then be fused , cemented or otherwise joined together by conventional means . on the barrel portion 1 of the syringe body 10 , at diametrically opposed positions , is a pair of finger - stop structures 5 , 5 . in the preferred embodiment shown in fig1 and 9 , each of the finger - stop structures has a distal barrier 6 and a proximal barrier 7 which define a region 8 therebetween , which region 8 is sufficiently wide and deep to accommodate an adult finger or thumb , so that the syringe barrel can easily be grasped in region 8 between the index and middle fingers ( if the practitioner chooses to operate the plunger with the thumb as shown in fig1 ) or between the middle finger and thumb ( if the practitioner chooses to operate the plunger with the index finger as shown in fig1 ). when the syringe barrel is grasped in region 8 between said fingers ( or between said finger and thumb ), slippage of the fingers down the barrel in a distal direction is blocked by the distal barrier 6 , while slippage up the barrel in a proximal direction is blocked by the proximal barrier 7 . thus the finger - stops are dual - directional : they impede slippage of the barrel - grasping fingers in both the distal and the proximal direction . in this they differ from the flange often seen at the proximal end of a conventional molded syringe barrel , which flange is designed to block slippage of the fingers in the proximal direction only . the finger - stop structures 5 , 5 need not be positioned at the extreme proximal end of the syringe body 1 , but may be positioned longitudinally at some intermediate place between the proximal and distal ends of the barrel portion 1 of the syringe body 10 . the finger - stop structures preferably are molded integrally with the rest of the syringe body 10 , as this avoids the extra manufacturing steps of separately making the finger - stop structures and of affixing them to the barrel ; but they can be made separately and affixed by conventional means such as bonding by heat or any suitable glue or cement . as is most clearly seen in fig1 , 9 and 11 , the finger - stop structures 5 , 5 do not occupy the entire circumference of the barrel in the longitudinal region thereof at which they are placed . instead they leave part of that circumference unobstructed , so that a calibration scale 11 can be inscribed longitudinally along the barrel continuously without hindrance or interruption , and without compromise to its legibility where the calibration scale passes into or through the longitudinal region of the barrel at which the finger - stop structures are placed . as is best seen in fig1 and 9 , the calibration scale does enter the longitudinal region where the finger - stop structures are , but the calibration scale occupies a different radial position than do the finger - stop structures , thus avoiding interference . this arrangement affords the practical advantage of avoiding unduly lengthening the barrel , as would be necessary if the entirety of the calibration scale had to be located distally of the finger - stop structures . unnecessary barrel length is undesirable for several reasons , including these : it compromises the goal of compactness of packaging , storage and shipping of the syringes , a consideration particularly important in disposable syringes , which are typically sold and used in large quantities and as to which the costs associated with packaging , shipping and storage are typically a more important consideration than with syringes designed to be reused ; it requires more material to manufacture a longer syringe barrel ( and a longer plunger assembly to cooperate with the longer barrel ), thus increasing cost and waste ; and a longer barrel requires greater length of travel of the plunger during the stroke , making the syringe less easily controllable and the plunger member ergonomically harder to operate in both directions with one hand . it will be appreciated that finger - stop structures much different from those shown in fig1 and 9 may be used instead . any pair of structures formed upon , attached to or impressed into diametrically opposed places on the barrel may serve the purpose of dual - directional finger - stops as long as those structures serve to inhibit slippage of the syringe - holding fingers in both the proximal and the distal direction along the barrel . among the alternative structures that could be employed as finger - stops at diametrically opposed places on the barrel are , for example , the following : patches of knurled , scored or otherwise roughened surface upon the exterior of the barrel ; dimples or depressions or other concavities in the exterior surface of the barrel ; or a pair of parallel , interrupted rings occupying a portion of the circumference of the barrel . even a single such interrupted ring , if located at a suitable longitudinal position intermediate between the proximal and distal ends of the barrel ( such as at region 8 indicated in fig1 and 9 ), would serve as an adequate dual - directional finger - stop , although some convenience would be sacrificed by the operator &# 39 ; s need to perform a grip - shifting maneuver in transitioning from the upward ( aspiration ) stroke to the downward ( injection ) stroke ; that is , the syringe - grasping fingers would have to be positioned above ( i . e ., proximally from ) the single interrupted ring so that it would serve as a barrier against slippage in the distal direction during the upward ( aspiration ) stroke but then shifted to a position below (( i . e ., distally from ) the ring so that it would serve as a barrier against slippage in the proximal direction during the downward ( injection ) stroke of the plunger . as seen in fig3 the plunger member 20 includes at its distal end a piston 21 , preferably made of rubber or other resilient material and preferably having at least one ring 22 which , when the plunger shaft 23 is inserted into the bore , forms a seal with the wall thereof which is impermeable to liquids and gases . at the proximal end of the plunger shaft 23 is a plunger button 24 , having associated therewith an inferior loop member 25 and a superior loop member 26 . the loop members are preferably made of a flexible plastic material and are preferably integrally molded with plunger button 24 , which in turn is preferably integrally molded with plunger shaft 23 . upon the superior surface of inferior loop member 25 , and preferably molded integrally therewith , are a series of whisker - like projections 27 . it will be appreciated that they do not project perpendicularly from the surface of said inferior loop portion , but at a slightly backward slant with reference to the distal end thereof . a corresponding series of whisker - like projections 28 is formed on the inferior surface of the superior loop member 26 . if desired , the inferior loop member 25 may be biased upwardly and the superior loop member 26 biased downwardly , so that in the structure &# 39 ; s resting state the superior surface of inferior loop member 25 bears against the inferior surface of superior loop member 26 , causing whisker - like projections 27 to engage the whisker - like projections 28 . alternatively , the two loop members may be biased so that they are spaced apart , as seen in fig3 but may be urged together to form a closed aperture which is tightened around , and securely holds , a finger or thumb inserted therethrough , as seen in fig4 . it will be appreciated that when the whisker - like projections 27 and 28 are engaged with each other , they cooperate in a ratchet - like manner , such that the loop aperture which loop members 25 and 26 define can be made smaller by sliding the superior loop member 26 distally ( leftwardly in fig3 ), but the structure resists sliding in the opposite direction . hence , the whisker - like projections cause the superior and inferior loop members to cooperate with each other in such a manner that the loop aperture can easily be made smaller but will resist being made larger when the whisker - like projections 27 and 28 are engaged with each other . as can best be seen in fig4 superior loop member 26 can be closed down upon inferior loop member 25 and , either by pulling superior loop member 26 in its distal ( i . e ., leftward , in fig4 ) direction or by pinching together the left and right sides of the loop formed by loop members 25 and 26 , a finger or thumb t can be snugly embraced within the loop aperture formed by the cooperation of said loop members . as can readily be seen , the two loop members may be slipped and slid with respect to each other so as to adjust the size of the aperture they form , thereby to accommodate a variety of differently - sized fingers and thumbs , making the loop adjustable to accommodate different practitioners &# 39 ; different finger sizes , and to accommodate each practitioner &# 39 ; s personal preference whether to operate the plunger with the index finger or with the thumb . it will also be appreciated that when the finger or thumb t exerts force upwardly in the direction indicated by arrow a1 in fig4 as it would if the finger or thumb t were being used to withdraw the plunger from the syringe barrel , as in performing the aspiration test , the whisker - like projections 27 , 28 will be pressed forcibly against each other , causing the loop aperture to resist opening . when the injection procedure is completed , finger or thumb t can be easily released simply by lifting up the distal end of superior loop member 26 in the direction of arrow a2 , shown in fig4 thereby disengaging the whisker - like projections 27 , 28 from each other and permitting the opening of the loop aperture and the easy release of the thumb or finger held within that aperture . alternatively , the finger or thumb may simply be withdrawn from the aperture of the loop without opening the loop . hence , an adjustable and easily releasable plunger loop is provided which serves to facilitate one - handed performance of the aspiration step . as should be apparent from the foregoing description , whisker - like projections 27 , 28 function as means for fastening loop members 25 and 26 together in a conveniently adjustable and releasable way . other means are available which are equivalent to , and may readily be substituted for , whisker - like projections 27 , 28 to achieve the adjustable and releasable fastening function thereof . for example , cooperating velcro ® fastener strips could be applied to the superior surface of loop member 25 and to the inferior surface of loop member 26 , in lieu of whisker - like projections . for another example , a strip coated on both sides with a pressure - sensitive adhesive could be applied to the superior surface of loop member 25 , or to the inferior surface of loop member 26 , or to both surfaces , in lieu of whisker - like projections . such adhesive strips are readily obtainable in the market . for instance , tape with pressure - sensitive adhesive on both sides , and flat , rectangular patches coated on both sides with pressure - sensitive adhesive , are widely available under brands including the scotch ® brand . these and virtually any like material could readily be adapted , by a person skilled in the art , to provide the desired adjustable and releasable fastening means . fig5 shows an alternative embodiment of an adjustable and easily releasable plunger loop . it is preferably made of a resilient , elastomeric plastic and is preferably molded of a single piece with the plunger shaft 23 , although it can be made separately and affixed at the proximal end of the shaft 23 by conventional means such as gluing , cementing or heat bonding . if desired , a plunger button 24 ( not shown in fig5 but indicated in fig1 and 3 ) can be provided in association with the plunger loop . the plunger loop of fig5 comprises an inferior loop member 40 and a superior loop member 41 which are biased to return to their resting state , as shown , and to form a loop which defines an aperture through which a thumb or finger can be inserted . preferably the diameter of the aperture thus defined is , in the loop members &# 39 ; resting state , small enough to fit snugly a small adult index finger . when the operator &# 39 ; s thumb or finger is inserted into the aperture , loop members 40 and 41 are displaced in a manner that expands the aperture to accommodate the thumb or finger ; but because the loop members are biased to return to their resting state , they exert springing forces which hold the finger or thumb securely , and the plunger loop they form resists opening and prevents escape of the thumb or finger during performance of the upward ( aspiration ) stroke of the plunger . when the injection procedure is complete , the thumb or finger is released simply by withdrawing it from the loop . it will be appreciated that whereas the embodiment of the adjustable plunger loop shown in fig3 and 4 employs whisker - like projections 27 , 28 to provide adjustability of the loop and resistance against opening during the aspiration step , the embodiment of fig5 depends principally on the springing forces exerted by loop members 40 and 41 to accomplish these purposes . another alternative adjustable plunger loop structure is illustrated in fig1 where loop members 30 and 31 , preferably formed integrally with plunger button 24 , are generally configured as overlapping arcs of a circle when in their resting state . loop members 30 and 31 are made of a resilient material , biased to return to their resting state after a load is withdrawn . in their resting state , loop members 30 and 31 define an aperture that is preferably no larger than a small adult index finger . when an index finger or thumb that is larger than the aperture is attempted to be inserted therein , loop members 30 and 31 are displaced sufficiently to accommodate the finger or thumb ; but because they are biased to return to their resting state , they exert a springing force upon the finger or thumb , embracing it snugly . when the thumb or finger so embraced is then lifted to exert a withdrawing force upon the plunger , loop members 30 and 31 retain it , enabling the accomplishment of the aspiration test . after that test , or the injection procedure , is complete , the thumb or finger may be withdrawn . loop members 30 and 31 in the embodiment shown in fig1 thus act similarly to loop members 40 and 41 in the embodiment shown in fig5 a difference , however , being that loop members 40 , 41 overlap in an &# 34 ; over - and - under &# 34 ; fashion while loop members 30 and 31 overlap in a &# 34 ; side - by - side &# 34 ; fashion . it will be appreciated that a single - arm loop structure could be employed , instead of either the two - overlapping - loop - members structure described above and shown in fig1 or the two - overlapping - loop - members structure described above and shown in fig5 . such a single - arm loop structure is shown in fig6 where single loop member 50 defines an aperture open at one side , rather than aperture closed on all sides . loop member 50 is preferably molded integrally with , but may be formed separately and affixed at the proximal end of , plunger shaft 23 . if desired , a plunger button 24 ( not shown in fig6 but indicated in fig1 and 3 ) may be provided in association with loop member 50 . loop member 50 is preferably made of a resilient , elastomeric plastic and it preferably forms an aperture which , in the resting configuration shown in fig6 has a diameter not larger than that of a small adult index finger . when the operator &# 39 ; s thumb or finger is inserted into the aperture , loop member 50 is displaced to accommodate that thumb or finger ; but because loop member 50 is biased to return to its resting configuration , it captures and snugly holds the finger or thumb and resists further opening when the finger or thumb is raised to perform the upward ( aspiration ) stroke . loop member 50 is preferably provided , at the free end thereof , with a detent 51 which serves to prevent escape of the thumb or finger from the open side of the aperture when the loop is under load , as when the captured finger or thumb is being used to apply a plunger - withdrawing force . yet another alternative for constructing an adjustable plunger loop is shown in fig7 and 8 . single loop member 60 is made of a flexible material , preferably a plastic , and is fixed at one end to the proximal end of plunger shaft 23 . it is preferably molded of a single piece with the plunger shaft , although it can be formed separately and attached to the plunger shaft by conventional means . loop member 60 may , if desired , be provided in association with a plunger button 24 ( not shown in fig7 and 8 , but indicated in fig1 and 3 ). at least the portion near the free ( distal ) end of loop member 60 has upon its superior surface , and preferably formed integrally therewith , a series of sawtooth projections 61 . ratchet housing 62 is preferably molded integrally with plunger shaft 23 but may be formed separately and attached by conventional means . when the free end of loop member 60 is conducted through ratchet housing 62 , a closed loop is formed through which the operator &# 39 ; s thumb or finger may be inserted . ratchet housing 62 is provided with a pawl 63 which comprises one or more sawtooth projections configured to mesh with those on loop member 60 . preferably , pawl 63 is also provided with a releasing tang 64 . pawl 63 is pivotably mounted within the ratchet housing and is biased to contact loop member 60 so that the sawtooth projections on loop member 60 mesh with one or more sawtooth projections on the pawl . preferably the mounting of the pawl , and its bias to engage the sawtooth projections on the loop member , are accomplished by making the pawl of a flexible material and forming it integrally with the ratchet housing . it will be appreciated that the cooperation of the loop member 60 with the pawl 63 provides a snare - like action , such that the loop can be easily adjusted to make the aperture smaller and tighten it around a finger or thumb which is inserted therethrough , but the loop resists opening under load . the tightening adjustment is accomplished by pushing or pulling the free end of the loop member 60 farther through the ratchet housing 62 . the pivotably mounted pawl rides over the sawtooth projections on the loop member and permits its passage so as to decrease the size of the aperture ; but when a withdrawing force is applied , the sawtooth projections on the loop member engage with one or more corresponding projections on the pawl and resist the enlargement of the loop aperture . after the injection procedure ( or the use of the syringe in a venous catheter - insertion procedure ) has been completed , the operator may simply withdraw the finger or thumb from the aperture . alternatively , the pawl may be provided with a tang 64 which affords the operator a convenient means to disengage the pawl from the loop member so as to permit the latter &# 39 ; s withdrawal from the ratchet housing and the enlargement of the plunger loop so as to facilitate withdrawal of the operator &# 39 ; s finger or thumb . it is within the skill of the art to devise a snare - like loop - size adjustment means which is simpler than that shown in fig7 and 8 but which will still work adequately for the purpose . for example , it is possible to dispense with the pivotably - mounted pawl and use instead a single ratchet tooth , mounted in or formed integrally with the roof ( that is , the side facing sawtooth projections 61 ) of the ratchet housing 62 , and to dimension the ratchet housing and tooth so that the tooth engages the sawtooth projections 61 on the loop member 60 . by varying the flexibility if the materials , or by varying the pitch of the ratchet tooth and the sawtooth projections 61 or the dimensions thereof , or the degree of interference therebetween , practitioners of skill in the art can readily arrive at a configuration which affords acceptable ease of closing the loop and an acceptable amount of resistance by the loop against opening under load . if both great ease of closing the loop and high resistance to opening are desired , the pitch of the sawtooth projections 61 and the ratchet tooth can be varied so that the pitch of the proximally - facing ( i . e ., toward the fixed end , and away from the free end , of loop member 60 ), sides of the sawtooth projections on the loop member 60 is much steeper than the pitch of the distally - facing ( i . e ., toward the free end of loop member 60 ) sides thereof . it will be appreciated that if the projections on the loop member are so configured they will cooperate with the ratchet tooth to provide a snare - like loop size adjustment means , in that the loop may easily be tightened by pulling on the distal end of loop member 60 to conduct it through ratchet housing 62 , but may not easily be loosened . thus the finger or thumb t may be secured snugly within the aperture defined by the loop member and may be withdrawn from the aperture thereafter without loosening it ; or , by applying sufficient force , the loop member may be made to withdraw partially from the ratchet housing so that the plunger loop loosens to facilitate withdrawal of the finger or thumb . as will be evident from the foregoing description , a practitioner using the syringe here disclosed for the injection of medicaments can easily and conveniently perform the aspiration test with a single hand , by performing the following steps : first the practitioner picks up the syringe by grasping the barrel between thumb and middle finger as shown in fig1 ( or , if preferred , between index and middle fingers as shown in fig1 ) in the region of the finger - stop structures . next , the practitioner inserts the index finger ( if the thumb is being used to grasp the barrel ) or the thumb ( if the index finger is being used to grasp the barrel ) through the loop aperture . next , the aperture is adjusted if necessary , as described above , to secure the plunger - operating finger ( or thumb ) snugly within it . the practitioner then loads the medicament into the syringe , measuring its amount with the syringe &# 39 ; s calibration scale if desired . using one hand to stabilize the patient &# 39 ; s arm ( or other injection site ), the practitioner then inserts the needle with the other hand . because the plunger - operating finger ( or thumb ) is secured within the adjustable loop aperture atop the syringe &# 39 ; s plunger member while the barrel is being securely grasped by other fingers of the same hand through the use of the finger - stops , the practitioner can easily draw the plunger backward to perform the aspiration test simply by raising the plunger - operating finger or thumb . if the test indicates that a blood vessel has been punctured , and intravenous injection of the medicament is not desired , then the practitioner withdraws the needle and starts over ; but if a blood vessel has not been punctured , then the practitioner proceeds with the injection in the usual way . a practitioner who desires to insert a catheter or tube into the lumen of a blood vessel can manipulate the syringe here disclosed in a similar manner , so far as the techniques of grasping the syringe barrel and engaging the plunger - operating finger or thumb with the plunger are concerned . the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof . the presently disclosed embodiments are therefore to be considered in all respects as being examples only , the scope of the invention being indicated by the appended claims rather than by the foregoing description , and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein .
disclosed is an ergonomically improved hypodermic syringe which facilitates one - handed use by allowing the same hand that holds the syringe to operate the plunger conveniently to accomplish both the distal stroke and the proximal stroke . the syringe includes a pair of finger - stop structures on diametrically opposite sides of the barrel which block slippage in both proximal and distal directions and which do not occupy the barrel &# 39 ; s entire circumference and do not interfere with the legibility of a calibration scale that passes through the region of the barrel with which said structures are associated . a loop atop the syringe &# 39 ; s plunger member is also provided , which is adjustable to vary the size of the aperture thereof for a snug fit with fingers and thumbs of varying sizes . in combination , the adjustable loop and finger - stops make the syringe plunger easily operable in both directions with one hand . the result is a syringe which is inexpensive to manufacture , which is compact to store and ship , and which enables an aspiration maneuver , to test for the presence of blood indicating that a blood vessel has been penetrated , to be performed easily with one hand .