while this invention is susceptible of embodiment in many different forms , there are shown in the drawing and will be described herein in detail specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated . a prior art pre - slit injection site 10 and associated blunt cannula 12 are illustrated in fig1 . the prior art injection site 10 has a cylindrical housing 14 with a fluid flow path 16 therethrough . a first end 18 of the housing 14 is closed with a relatively thin disc - shaped resealable member 20 . the member 20 has a resealable opening 22 therein . the member 20 is a molded septum with an integrally formed skirt 20a . the skirt 20a is oriented generally perpendicular to the portion of the septum with the opening 22 . the cannula 12 includes a body portion 24 which carries at a first end a hollow , cylindrical , blunt piercing member 26 . as the cannula 12 is moved in a direction 28 toward the first end 18 of the injection site 10 , the member 26 slidably engages the opening 22 . the sealing member 20 is then deformed adjacent the opening 22 and the member 26 extends into the flow path 16 . a fluid flow path through the cannula 12 will then be in fluid flow communication with the flow path 16 via the hollow piercing member 26 . in contradistinction to the prior art pre - slit injection site 10 of fig1 fig2 a and 2b illustrate a pre - slit injection site 34 being coupled to a peripheral venous catheter 36 . the catheter 36 is shown in fluid flow communication with a vein in a hand h of a patient . the catheter 36 carries at a proximal end 38 a luer - type female twist lock connector 41 . the pre - slit injection site 34 is formed with a cylindrical housing 40 having a first end 42 and a second end 44 . carried by the housing 40 , adjacent the second end 44 is a hollow cylindrical fluid flow member 46 . the member 46 slidably engages a receiving member in the housing 38 of the catheter 36 , thereby providing a sterile fluid flow coupling as is well known and conventional . a plurality of internal male luer - type threads 48 is carried by the housing 40 adjacent the second end 44 . the threads 48 will engage the flange member 41 when the injection site 34 is rotated in a direction 50 . when so coupled together , the catheter 36 and the injection site 40 provide a sealed coupling through which fluids may be injected into the vein of the hand h . fig3 illustrates , in section , further details of the injection site 34 . a resealable septum 52 is carried by the first end 42 of the housing 40 . the septum 52 includes first and second spaced apart surfaces 54 and 56 respectively . the surface 54 has been forced into a dome - like shape by annular , u - shaped , swaged end members 58 carried by the first end 42 . the dome - like shape of the surface 54 can extend beyond a surface 42a of the first end 42 . this facilitates cleaning the surface 54 . the septum 52 has a generally cylindrical shape . the septum 52 can be formed of a latex or synthetic rubber material . alternately , the septum can be formed of a thermoplastic elastomer . the material used for the septum 52 should be non - toxic and sterilizable such as by means of radiation , steam or eto . because the septum 52 is generally cylindrical in shape , it can be die - cut from a sheet , cut from an extruded rod or molded . the septum 52 can have an exemplary diameter on the order of 0 . 30 inches . the height of the septum 52 can be , for example , on the order of 0 . 125 inches . the first end 42 is also formed with a tapered interior surface 60 which terminates in an annular channel 62 . the tapered interior surface 60 has a taper in a range of 5 degrees to 20 degrees . preferably , the taper will be on the order of 12 degrees . with the indicated size of the above noted exemplary septum 52 and a 12 degree taper , diametric resealing compression of the septum 52 adjacent the channel 62 is on the order of 10 %. the channel 62 is bounded in part by a septum supporting ridge 62a . the channel 62 can typically have a depth in a range of 0 . 050 - 0 . 070 inches . a peripheral surface 64 of the septum 52 slidably engages the tapered interior surface 60 as the septum 52 slides into the first end 42 . the annular channel 62 which underlies the interior peripheral surface 56 of the septum 52 is provided to permit the septum 52 to deform when a blunt cannula is inserted through an opening 66 therein . the housing 40 is also formed with a fluid flow path 68 such that fluids injected via a blunt cannula inserted through the resealable opening 66 can flow into the catheter 36 for delivery to hand h of the patient . the swaged end members 58 apply axial forces to the septum 52 thereby creating the domed exterior peripheral surface 54 . the axial forces applied by the end members 58 slightly deform the regions 52a and 52b . in contradistinction , the tapered internal surface 60 applies radially directed forces to the septum 52 , thereby forcing the opening 66 into a resealed condition . as shown in fig3 an axial height of the ridge 62a defines an annular channel 62b . the region 52a of the septum 52 is partially deformed into the annular channel 62b by the end member 58 applying axial forces to the 62b by the end member 58 applying axial forces to the septum 52 . as shown in fig4 b . the septum 52 deforms farther into the annular channel 62b , and into channel 62 , when the blunt piercing member 98 is inserted through the opening 66 . referring to fig1 - 26 , the resealable septum is moveable from a first position contacting the annular ridge and outside the annular channel prior to compression to a second position contacting the annular ridge and extending into the annular channel after compression . in an alternate embodiment , the surface 54 could be formed as a flat , as opposed to a domed , surface . as also shown in fig3 the first surface 54 is proximate the first end 42 . more particularly , the first surface 54 is proximate an axially outermost portion 42b of the surface 42a . in this manner , the first surface 54 can be easily cleaned , i . e . easily wipeable . as discussed above , the first surface 54 may be dome shaped , and in an alternate embodiment , flat shaped . also shown in fig3 the first end 42 of the injection site 34 includes a portion 42c extending from the axial direction to a radially inward extending portion 42d . the radially extending inward portion 42d has a thickness 42e in the axial direction . the thickness 42e is defined in the axial direction at the axially outermost portion 42b of the surface 42a . accordingly , the first surface 54 is a relatively short distance from the axially outermost portion 42b of the surface 42a . in other words , the distance from the axial outermost portion 42b to at least a portion of the first surface 54 is less than the thickness 42e of the radially inward extending portion 42d . thus , the surface 54 is easily wipeable . once the injection site 34 is lockingly engaged with the catheter 36 , a sealed system is formed through which fluids can be infused into the catheter 36 . the resealable septum 52 closes the fluid flow path 68 . fig4 a and 4b illustrate in combination the injection site 34 , a blunt shielded cannula 80 and a syringe of a conventional type 82 . the syringe 82 , as is well known , can be formed with a cylindrical hollow end 84 which carries a male luer - type twist lock thread 86 . a hollow centrally located cylindrical fluid flow member 88 is in fluid flow communication with an interior region 90 of the syringe 82 . the shielded blunt cannula 80 carries at a first end 92 a female luer twist - lock flange 94 . the flange 94 will slidably engage the threads 86 of the end 84 . hence , the shielded blunt cannula 80 can be locked to the syringe 82 forming a closed fluid flow pathway . the shielded cannula 80 could alternately be formed fixedly attached to the syringe 82 . the shielded blunt cannula 80 carries a cylindrical hollow protective shield 96 which surrounds a centrally located hollow , elongated cylindrical blunt piercing member 98 . the cylindrical blunt piercing member 98 has a total length on the order of 3 times the thickness of the septum 52 in order to ensure complete penetration . the cylindrical blunt piercing member 98 has a diameter on the order of 1 / 3 the diameter of the septum 52 . the shield 96 is desirable and useful for maintaining the piercing member 98 in an aseptic condition by preventing touch contamination prior to the shielded cannula 80 engaging the pre - slit septum 52 . also , the shield helps to align the piercing member with the pre - slit septum . the cylindrical blunt piercing member 98 can slidably engage the pre - slit septum 52 , best illustrated in fig4 b , thereby extending through the preformed opening 66 therein . as illustrated in fig4 b , when the piercing member 98 slidably engages and pierces the septum 52 , the region 52a deforms by expanding into and filling , at least in part , the annular channel 62 . as can be seen in a comparison between fig3 and 4b , the resealable septum 52 has a sealing surface 66a defined by the resealable opening 66 . the sealing surface 66a extends in an axial direction prior to insertion of the blunt piercing member 98 through the septum 52 and remains in the axial direction after insertion of the piercing member 98 through the septum 52 . as shown in fig4 b , the axial length of the sealing surface 66a of the resealable opening 66 increases when the piercing member 98 is inserted through the septum 52 . the deformation facilitates insertion of the piercing member 98 through the slit 66 . subsequent to the piercing member 98 slidably engaging the injection site 34 , the interior region 90 of the syringe 82 is in fluid flow communication with the flow path 68 of the injection site 34 via flow paths 88a and 99 respectively of the syringe and the blunt piercing member 98 . in this engagement condition , the septum 52 seals completely around the piercing member 98 . hence , exterior gases , liquids or airborne matter will be excluded from the channel 68 . subsequent to infusing fluid from the syringe 82 into the fluid flow pathway 68 , hence into the catheter 36 and the hand h of the patient , the syringe 82 with lockingly engaged shielded cannula 80 can be slidably withdrawn from the injection site 34 . subsequent to this withdrawal , the septum 52 reseals the opening 66 therein . the opening 66 will repeatedly reseal , when the piercing member 98 is removed , provided that the pressure ( in the septum 52 of the opening 66 ) created by interaction of the septum material properties and compression supplied by the housing exceeds the pressure challenge of the fluid contained within . blunt cannula do not haphazardly core , lacerate , or otherwise damage the sealing interface 66 as conventional needles do , thereby allowing repeatable resealability . however , septum material properties , thickness , and compression allow resealability for a finite number of conventional needle insertions . the combination injection site 34 and catheter 36 then return to its pre - infusion , sealed condition . fig5 a and 5b illustrate the pre - slit injection site 34 used in combination with a blunt cannula 80a . the cannula 80a includes a hollow body portion 92a with a luer flange 94a , a piercing member 98a , and manually operable elongated locking members 100a and 100b . alternately , a tubing member could be affixed to the hollow body portion 92 . curved end regions 100c of the members 100a and 100b slidably engage the second end 44 of the housing 40 when the piercing member 98a of the blunt cannula 80a has been forced through the pre - formed opening 66 , best illustrated in fig5 b . the embodiment illustrated in fig5 a and 5b has the advantage that the infusing cannula 80a cannot accidentally disengage from the pre - slit septum 34 during the fluid infusion process . it will be understood that while spring - like deflecting members 100a and 100b are illustrated in fig5 a and 5b that other forms of locking members are within the spirit and scope of the present invention . fig6 illustrates an alternate pre - slit injection site 34a . a tubing member 102 can be fixedly attached to the cylindrical hollow fluid flow member 46 . the embodiment 34a of fig6 utilizes the same structure for the septum 52 including the tapered surface 60 and the underlying annular channel 62 as does the embodiment 34 in fig3 . the shielded cannula 80 can be utilized with the injection site 34a as previously described . in the event that it is desirable to infuse solution from a container 104 with a conventional port 106 , a fluid administration set 110 of a conventional variety may be utilized . the set 110 includes a spike connector 112 at a first end . the spike connector 112 is designed to pierce the port 106 of the container 104 . the set 110 can also carry a slidably engageable connector 114 of a known type at a second end . as illustrated in fig7 the connector 114 can slidably engage the first end member 92 of the shielded cannula 80 , thereby placing the interior fluid of the container 104 into fluid communication with the tubing member 102 . fig8 illustrates yet another alternate 80b to the shielded cannula 80 . the piercing member 98b carries a tubing member 118 fixedly attached thereto . the tubing member 118 could be coupled at a second end to a container such as the container 104 . the present pre - slit injection site can be directly affixed to a container 120 as illustrated in fig9 . the container 120 includes a rigid hollow cylindrical access port 122 affixed thereto . the access port 122 includes a fluid flow channel 124 in fluid flow communication with the interior of the container 120 . sealingly affixed to the port 122 is a pre - slit injection site 126 . the site 126 includes a cylindrical housing 128 which carries at a first end 130 a septum 132 with a slit 134 formed therein . the first end 130 has been swaged to form an annular u - shaped retaining member 136 . the retaining member 136 in turn forms a domed exterior peripheral surface 138 on the septum 132 . the first end 130 also includes a tapered interior force applying surface 140 and an annular channel 142 underlying the septum 132 . as discussed previously , the channel 142 provides a space into which the septum 132 can deform when a blunt cannula is forced through the resealable opening 134 . further , as illustrated in fig9 the injection site 126 can be covered by a removable cover 146 of a type used with the conventional port 106 of the bag 120 . while the bag 120 is illustrated formed with two ports , the conventional pierceable port 106 and the pre - slit injection site 126 , it will be understood that as an alternate ( fig1 ), a container 150 could be formed which includes only the pre - slit injection port 126 . the removable cover 146 could be used in combination with the container 150 . as illustrated in fig1 , the pre - slit injection site 126 can be utilized for the purpose of injecting fluid from the syringe 82 , coupled to the shielded cannula 80 , into the container 150 . when so utilized , the blunt piercing member 98 is used to place the interior fluid containing region 90 of the syringe into fluid flow communication with the interior of the container 150 . fig1 and 13 illustrate a fluid flow coupling system 151 having as a first element a pre - slit injection site 126a . the site 126a is the same as the site 126 except for a plurality of exterior threads 153 formed on an exterior peripheral surface 155 of the housing 128a . a second element of the coupling system 151 is a shielded blunt cannula 157 . the shielded blunt cannula 157 is sealingly affixed to a flexible tubing member 159 by means of a proximal hollow cylindrical member 161 . the member 161 extends into a hollow cylindrical shield 163 to form a blunt piercing member 165 . the shield 163 carries , on an interior peripheral surface , a set of coupling threads 149 . the threads 149 match the threads 153 . the two connector elements 126a and 157 slidably engage one another when the shielded cannula 157 moves in an axial direction 167 toward the injection site 126a . the blunt piercing member 165 penetrates the septum 132a . the coupling member 157 can then be rotated in a direction 169 such the interior set of threads 149 carried thereon engages the exterior set of threads 153 . as a result , the two coupling members 126a and 157 are lockingly engaged together with the insertion member 165 extending through the opening 134a in the septum 132a . hence , fluids can flow from the container 150a via the connector system 126a and 157 through the tubing member 159 to the recipient . injection sites of the type described above are also usable in connection with other fluid flow coupling components . for example , with respect to fig1 , a pre - slit injection site 160 of the type described above can be used in combination with a spike connector 162 of a conventional variety . spike connectors such as the spike connector 162 can be used to pierce conventional ports such as the port 106 of the container 104 ( fig6 ). when the spike connector 162 is so used , the pre - slit injection site 160 can then be utilized for the purpose of coupling to other fluid administration sets . the injection site 160 illustrates an alternate form of swaging the first end 42c for the purpose of retaining the septum 52c therein . the first end 42c can be swaged so as to form an annularly shaped , spiral , spring - like member 164 . the member 164 has a free end 164a which engages the exterior dome - shaped peripheral surface 54c of the septum 52c . the spiral , spring - like swaged member 164 will tend to uncoil , thereby continuously applying axial force to the septum 52c and maintaining the domed exterior peripheral surface 54c . in yet another alternate , fig1 illustrates a pre - slit injection site 166 formed in a y - junction member 168 . the y - junction member 168 is fixedly attached to first and second tubing members 170 and 172 respectively . as an alternate to forming the slit 66 completely through the septum 52 , as illustrated in fig1 , a slit 66e can be formed only partly through the septum 52e . such a structure has the further advantage that , until used for the first time , the septum 52e is completely sealed . the septum 52 can be formed in two parts . one part can have a slit , such as the slit 66 , extending entirely therethrough . a second part can be formed without a slit . these two parts can be located adjacent one another in the first end 42 of the injection site . the slit 66 may be longer on the top of the septum than the bottom . this feature aids blunt cannula alignment with the slit upon insertion , and aids resealability by minimizing the critical slit sealing interface area . in accordance with the present invention , the slit could have a length with a range on the order of 0 . 03 to 0 . 150 inches . preferably , a slit length on the order of 0 . 07 inches will be used in combination with a blunt cannula having a diameter on the order of 0 . 1 inches . when initially used , the blunt cannula piercing member , such as the member 98 , will be forced through the slit 66a . the lower peripheral surface 56e will then be punctured , providing access for the blunt cannula piercing member 98 into the fluid flow pathway 68e . pre - slit injection sites of the type described above can be utilized in combination with burette solution administration sets . one such set 176 is illustrated in fig1 . the set 176 includes a pre - slit injection site 178 of the type described above . the injection site 178 is affixed to an exterior planar surface 180 of the burette 182 . a removable cover 184 can be used to maintain the injection site 178 in an aseptic condition until blunt cannula 186 or 188 is inserted therethrough . fig1 - 23 disclose a method of making a pre - slit injection site in accordance with the present invention . in a first step , a housing 200 is provided . the housing 200 has an interior tapered surface 202 at a first end 200a thereof . the interior peripheral surface terminates in an annular channel 204 . a cylindrical septum 206 can be provided adjacent the end 200a . in a second step , the septum 206 can be forced into the end 200a of the housing 200 and slightly deformed by the tapered peripheral surface 202 using an axially moving die 210 . when positioned by the die 210 , the septum 206 is located adjacent an internal annular ring 212 which bounds the annular channel 204 . in a third step , a second die 214 can be utilized to swage the end 200a into spiral - shaped , spring - like members 200b which apply axially directed forces against an exterior peripheral surface 206a of the septum 206 . the axially directed forces form the flat surface 206a into a domed exterior peripheral surface 206b as illustrated in fig2 . simultaneously , with swaging the end members 200a so as to lock the septum 206 into the housing 200 and to form the domed exterior peripheral surface 206b , a knife 216 can be utilized to form a slit in the septum 206 . alternatively , the slit may be cut by a separate die in a separate step . if the septum 206 is formed as an extrusion , the slit can be created during the extrusion process . if the septum 206 is formed by stamping from a rubber sheet , the slit can be cut during the stamping process . if the septum 206 is formed by compression molding , the slit can be cut during the trimming process . in order to extrude the slit into rod , a flat pin extrusion bushing can be used . a trailing ribbon may be attached to the bushing . the ribbon would prevent curing material across the slit . the ribbon or wire could be placed in the rod core and later stripped out leaving a slit . an inert substance , such as silicone oil , could be coextruded in the center of the rod to prevent curing across the slit and provide lubrication and a visible target for cannula insertion . fig2 and 25 illustrate alternate swaging steps wherein a die 220 moving axially toward the housing 200 swages the end region 200a so as to form an annular u - shaped region 200c and the exterior domed peripheral surface 206c . the dies 214 or 220 can be formed with various alternate shaped swaging surfaces 224 , as illustrated in fig2 , depending on the precise shape of the end swage which is desired . it will be understood that all such variations in the swaging operation are within the spirit and scope of the present invention . the injection site configuration need not be limited to the configurations depicted in fig3 - 5b , 9 , 12 - 16 . rather , several configurations could be constructed without departing from the scope of this invention . any such configuration would provide a flexible preslit sealing member captured in a housing which provides compression to create a seal against pressure and a void region to accommodate deformed portions of the sealing member material only when the material is deformed or displaced by a blunt cannula piercing member . one such possible configuration is depicted in fig2 and 28 . fig2 and 30 illustrate a tapered cannula structure 250 which is an alternate to the tapered cannula 98 . the cannula 250 includes a proximal end 252 with an interior region 254 . the region 254 is in part bounded by an internal peripheral wall 256 which is formed with a standard luer taper . the tapered cannula 250 can be formed with a luer - type coupling flange 257 at the proximal end so as to be releasably connectable to the syringe 82 as was the tapered cannula 98 previously discussed . extending from the proximal end 252 is a cylindrical tube having a cylindrical mid - region 258 and a distal end member 260 . the member 260 has a generally elongated , cylindrical shape with an exterior side wall 262 . a centrally located , cylindrical , internal fluid flow path 264 extends through the distal end member 260 and mid - region 258 in fluid flow communication with the interior region 254 . the distal end of the end member 260 has a tapered exterior surface 266 . the tapered exterior surface 266 minimizes insertion force as the cannula 250 is being forced through a slit of a septum , such as the slit 66 in the septum 52 . the angle of taper of the surface 266 is preferably in a range between 25 to 45 degrees . the member 260 is also provided with a plurality of elongated grooves 268 . the grooves 268 in the exterior wall of the member 260 decrease the surface area of contact at the cannula / septum interface during insertion of the cannula into the injection site 34 . this reduced exterior contact surface area decreases the frictional component of the insertion force . in one embodiment , the tapered blunt cannula 250 may have overall insertion length , corresponding to combined axial lengths of mid - region 258 and end member 260 , on the order of 0 . 375 inches . an alternate cannula structure 280 is illustrated in fig3 , 32 and 33 . the cannula structure 280 includes a proximal end region 282 corresponding to the end region 252 of the cannula 250 . the region 282 includes a luer flange 283 . the cannula 280 also includes a central , elongated , cylindrical region 288 . the central region 288 carries at a distal end thereof an elongated cylindrical end member 290 . the member 290 includes an exterior , peripheral , cylindrical surface 292 ( fig3 ). the surface 292 is interrupted by a plurality of spaced - apart , elongated slots or apertures 294 . the slots 294 are defined by first and second spaced - apart , elongated , parallel side surfaces 294a and 294b . each of the slots terminates in an end surface 294c at the central region 288 . a fluid flow path 294d extends through the cannula 280 . the flow path 294d is in fluid flow communication with the slots 294 . between the slots 294 , at a distal end of the region 290 , the exterior surface 292 terminates in tapered end regions 298 to facilitate insertion of the cannula into a pre - slit injection site . the slots 294 themselves also function to decrease the surface contact area , and this further minimizes the insertion force . the slots 294 are oriented substantially 90 degrees apart around a longitudinal axis 300 . the slots 294 increase the internal flow path cross - section . this increases the fluid flow rate . the slots 294 also provide for enhanced dispersion characteristics owing to the fluid flowing radially out through the slots 294 . this radial flow , effecting a change in fluid flow direction of about 90 degrees , promotes flushing and dispersion of fluid through the injection site 34 . another embodiment of a blunt cannula 310 is illustrated in fig3 - 37 . the cannula 310 is formed with an enlarged proximal connection region 312 corresponding to the region 252 of the cannula 250 . the region 312 includes a luer flange 313 and a central fluid flow region 314 . an intermediate , cylindrical region 318 extends from the proximal connection region 312 . the cylindrical intermediate region 318 includes a fluid flow path 320 in communication with the fluid flow region 314 . the end region 324 extends from the region 318 and includes a first cylindrical portion 326 into which the fluid flow path 320 extends . the region 326 terminates in a tapered exterior surface 328 . the tapered exterior surface 328 merges with a centrally located lead post or guide post 330 . the lead post 330 terminates in a hemispherical end surface 332 . the lead post 330 helps locate the septum slit 66 prior to insertion and facilitates penetration of the septum slit 66 by the cannula . the lead post 330 facilitates insertion by providing a very low insertion force at the beginning of the insertion step as the cannula is pushed through the slit , such as the slit 66 . in a preferred embodiment , the guide post 330 can have a length on the order of 0 . 060 inches and a diameter on the order of 0 . 050 inches . the end region 318 includes a novel structure for increasing the flow rate and enhancing dispersion characteristics . in particular , the region 318 includes three radially oriented slots 338 . each slot 338 has sides 339a and 339b which each lie along a radius of the cylindrical portion 326 as best illustrated in fig3 . the fluid flowing through the cannula 310 undergoes a change in direction ( of up to about 90 degrees relative to the cannula center line 337 ) in the slots 338 . this change in direction increases fluid dispersion . further , since the slots 338 open radially , fluid flow can be maintained even if the end surface 332 of the cannula is pushed up against any material in the system in which the cannula is inserted . another embodiment of the tapered cannula of the present invention is illustrated in fig3 - 40 and is designated generally therein by reference numeral 340 . the cannula 340 includes a proximal end 342 which can include a luer coupling flange 344 for cooperating with a suitable mating structure on a syringe . the proximal end 342 also defines an interior region 346 . extending from the proximal end 342 is a generally cylindrical mid - region 348 . extending from the mid - region 348 is an end member or region 350 which includes a tapered surface 352 . the distal end of the end region 352 terminates in a blunt , arcuate end surface 356 . defined within the mid - region 348 and end region 350 is an internal fluid flow channel 354 which communicates with the interior region 346 . fluid discharges from the flow channel 354 via grooves or apertures 358 in the end region 350 . the change in direction of the fluid flow as the fluid passes from the interior channel 354 through the apertures 358 improves fluid dispersion with respect to mixing or flushing in the system downstream of the cannula ( e . g ., the injection site , drug vial , etc .). the apertures 358 may also function to increase withdrawal force or tug resistance . moreover , since the fluid passes radially out through the apertures 358 , fluid flow through the cannula 340 can be maintained even when the distal end surface 356 of the cannula is bottomed out or pushed against any material in the system in which the cannula is inserted . the structure of the cannula 340 is adapted to be constructed with a minimal lead post length ( i . e ., the portion of the cannula distal end between the end surface 356 and the interior flow channel 354 ). further , the design accommodates the use of a minimal tip diameter , minimal taper angle , and minimal cannula diameter . the minimization of these parameters results in a decrease in the peak insertion force required to properly install the cannula in the injection site . preferably , the total cross - sectional flow area through the three apertures 358 is about three times the cross - sectional flow area of the interior channel 354 . this enhances the flow rate capability compared with a simple open ended cylindrical flow channel of equal length . the design of the cannula 340 also is effective in reducing or limiting &# 34 ; kick back &# 34 ; or recoil of the cannula after insertion . the resilient material of the septum in an injection site can subject the cannula to forces tending to push the cannula back out of the septum . the kick back forces on the cannula 340 are minimized by the provision of the generally cylindrical mid - region 348 . another embodiment of the cannula of the present invention is illustrated in fig4 and 42 wherein the cannula embodiment is designated generally therein by the reference numeral 360 . the cannula 360 includes a proximal end 362 defining an interior region 364 and having a luer flange 366 for connection to a suitable mating engaging structure . a generally cylindrical mid - region 366 extends from the proximal end 362 , and a end region 368 extends from the mid - region 366 . as with the previous embodiment of the cannula 340 illustrated in fig3 - 40 , the embodiment of the cannula 360 minimizes kick back or recoil owing to the provision of a substantially cylindrical mid - region 366 . this design also increases withdrawal or tug resistance . a generally cylindrical internal flow channel 370 extends through the end region 368 and mid - region 366 in communication with the interior region 364 of the proximal end region 362 . the end region 368 is provided with a tapered surface 372 . the design permits the use of a very small taper to minimize the insertion force . further , the design permits the cannula 360 to be constructed with a small tip diameter , small taper angle , and small cannula diameter so as to reduce the peak insertion force . another embodiment of the cannula of the present invention is illustrated in fig4 - 44 and is designated generally therein by reference numeral 380 . the cannula 380 includes a proximal end 382 with a luer flange 384 . an interior fluid flow region 386 is defined on the interior of the proximal end 382 . extending from the proximal end 382 is a mid - region 388 . a distal end region 390 extends from the mid - region 388 . an internal fluid flow channel or path 392 extends through the end region 390 and mid - region 388 , and is in communication with the interior flow region 386 . the end region 390 has an exterior tapered surface 394 . this facilitates insertion of the cannula into the injection site . in contrast , the mid - region 388 is generally cylindrical so as to minimize kick back and increase the withdrawal force or tug resistance . further , to provide even greater withdrawal force , the mid - region 388 includes an annular barb 396 . the barb 396 has a sufficient radius so as to preclude damage to the septum of the injection site and so as to accommodate molding in a straight - draw tool . the maximum diameter of the annular barb 396 may typically be on the order of 0 . 02 inches greater than the diameter of the cylindrical mid - region 388 . although the barb 396 functions to prevent inadvertent removal of the cannula 380 from the septum of the injection site , removal of the cannula 380 can still be achieved by exerting a sufficiently great axially directed removal force on the cannula 380 . still another embodiment is illustrated in fig4 which includes a blunt tapered cannula insertion member 400 for insertion into a pre - slit injection site , the cannula 400 having a distal end region 402 with a tapered exterior surface which in the preferred embodiment is an approximately 8 ° taper . the defined aperture 404 for fluid flow is disposed at the end 406 of the distal end region 402 . the end 406 includes a radiused tip defined by a radius of approximately 0 . 01 inch . the radiused tip reduces insertion force , assists in locating the slit in the injection site and in addition has the practical advantage of facilitating complete filling of the cannula mold cavity . the tapered surface of the distal end region 402 has an axial length of approximately 0 . 10 &# 34 ; in the preferred embodiment . adjacent to the tapered distal end region is a generally cylindrical region 408 for entering into the injection site behind the distal end region 402 , thereby reducing kick back during insertion . the generally cylindrical region 408 has a small draft angle such as about one - half degree . the force required to insert any of the above - discussed embodiments of the blunt tapered cannula into the septum of the injection site depends upon a number of factors : friction at the cannula / septum interface , cannula diameter , cannula taper angle , and degree of septum compression . the cannula / septum interface friction is , in turn , dependent upon lubrication , if any , material properties , and surface finish . it will be understood that the friction at the cannula / septum interface can be reduced by providing a smoother surface finish on the cannula ( e . g ., by sand blasting the cannula exterior surface ) or by molding the cannula so as to produce a matte finish . conventional lubricants can also be used to further reduce the friction and thereby lower the insertion force required . in the embodiments of the cannulae described herein , the mid - region and the tapered distal end region may be alternatively characterized as together forming at least one tube defining a fluid flow path therein with the tube having a distal end region for penetrating the injection site . in preferred contemplated embodiments , the exterior surface of the distal end region may have a taper angle as small as between one and fifteen degrees . further , a locking means , such as the locking arms 100a , 100b discussed with reference to fig5 a and 5b , may be provided on the cannula embodiments illustrated in fig2 - 45 to permit the cannulae to be releasably locked to the injection site . the above described insertion members , usable as part of a blunt cannula , are preferably molded of a plastic formulation including silicone or other lubricant . the use of silicone or other lubricant increases the ease of insertion of that member into the pre - slit injection site . from the foregoing , it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the novel concept of the invention . it is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred . it is , of course , intended to cover by the appended claims all such modifications as fall within the scope of the claims .
a pre - slit injection site includes a housing with a flow path therethrough . a first end of the housing carries a pre - slit septum . one form of a blunt cannula , usable with the injection site , carries a locking member . when the pre - slit injection site slidably receives the blunt cannula , the locking member latches to the injection site and creates a mechanically coupled unit . another form of the cannula includes a tube having a tapered distal end region and having elongate discharge slots for reducing contact surface area and for directing the flow laterally out of the cannula . the cannula may also include a rounded lead post , an annular barb , and axially oriented grooves .