the injection syringe shown in fig1 , 5 and 6 includes a cylindrical or tubular syringe body 1 and a cylindrical piston 10 which is arranged in the syringe body 1 in such a manner that it can be displaced therein . a conical holding device 7 for an injection needle 6 is located at the front end of the syringe body 1 . the injection needle 6 can either be detachable or fixed . the piston 10 consists of two piston elements 2 and 3 which can be displaced in relation to each other along the longitudinal axis of the syringe body 1 . the outer diameter of the first piston element 2 corresponds to the inner diameter of the syringe body 1 . a piston rod 4 is mounted on the side of the first piston element 2 which is remote from the injection needle 6 . a central channel 8 , in alignment with the longitudinal axis of the syringe body 1 and having a constant diameter , runs through the piston rod 4 and the first piston element 2 . the second cylindrical piston element 3 is arranged in this central channel 8 in such a manner that it can be displaced . the outer diameter of the second piston element 3 corresponds to the inner diameter of the central channel 8 . a piston rod 5 is also mounted on the side of the second piston element 3 which is remote from the injection needle 6 . on the syringe body 1 there is a coarse scale ( fig1 ) having a gradation of 1 ml for example . the piston rod 5 of the second piston element 3 is marked with a fine scale having a gradation of 0 . 05 ml for example ( fig1 ). if an injectable solution is drawn up with this injection syringe , the end of the injection needle 6 is immersed into an ampoule or vial containing an active ingredient , and the second piston element 3 is slightly pulled out of the central channel 8 of the piston rod 4 of the first piston element 2 . thus , a vacuum is created in the central channel 8 and the active ingredient flows from the ampoule through the injection needle 6 into the central channel 8 ( fig5 ). this guarantees that the active ingredient can be drawn up with a precision of 0 . 05 ml since the piston rod 5 has such a gradation . if more than one milliliter of the strong active ingredient , for example 1 . 25 ml , are to be drawn up , this scale and the scale on the body 1 will be used together . after the active ingredient has been drawn up , the injection needle 6 is immersed into a diluent , and the first piston element 2 is displaced by pulling the corresponding piston rod 4 in a direction opposite to the injection needle 6 . thus , the necessary amount of diluent can be drawn up ( fig6 ). in the embodiment of the injection syringe shown in fig2 and 4 the conical holding device 7 for the injection needle 6 is located at the area of edge of the front end of the syringe body 1 . the piston consists of two adjacent piston elements 2a and 3a both of which have the form of a cylindrical segment . the front part thereof , which in general is circular , is limited by a straight chord 11 and 13 , respectively . when both piston elements 2a and 3a and their straight chord 11 , 13 are adjacent to each other they form a complete cylinder , with the outer diameter thereof corresponding to the inner diameter of the syringe body 1 . thus , the outer surfaces of both piston elements 2a , 3a are in contact with the inner surface of the syringe body 1 . the cylindrical syringe body 1 is marked with scales of different gradation ( not shown ). a piston rod 4a and 5a , respectively , is arranged at the side of each of the piston elements 2a , 3a which is remote from the injection needle 6 . each of the piston rods 4a and 5a have a surface 14 and 15 , respectively lying in extension of the corresponding chord , the surface being parallel to the longitudinal axis of the syringe body 1 . by these surfaces 14 , 15 it is possible that both piston elements 2a and 3a can be disposed in relation to each other along the longitudinal axis of the syringe body 1 . the piston element 3a , the front surface of which is considerably smaller than the front surface of the first piston element 2a , is located directly before the conical holding device 7 . an injection solution is drawn up with the injection syringe shown in fig2 and 4 in the same manner as with the injection syringe shown in fig1 .
the injection syringe which is particularly used for medical purposes . the syringe has a body , a piston which is disposed in the syringe body for displacement therein and an injection needle . the piston has at least two piston elements , 3 which are displaceable in relation to each other along the longitudinal axis of the syringe body .