INJECTION INTO THE CIRCULATION. 217 



For operations requiring exact dosage experience 

 has led me to prefer a syringe after the pattern of C, 

 in Fig. 47 i. e., of the form commonly used by physi- 

 cians. The reason for this is as follows : in making 

 hypodermic injections or injections into the circulation 

 there is a certain amount of resistance to the passage of 

 fluid from the needle. If one overcomes this resistance 



FIG. 47. 



Forms of hypodermic syringe. 

 A. Koch's syringe. B. Syringe of Strohschein. C. Overlack's form. 



by means of a cushion of compressed air, as is the case 

 in syringes A and B of Fig. 47, the sudden expansion 

 of the air in the body of the syringe when resistance is 

 overcome frequently causes a larger amount of fluid 

 to be ejected from the needle than is desired. No 

 such accident is likely to occur when the fluid is forced 

 from the barrel of the syringe by the head of a close- 

 fitting piston, with no air intervening between the fluid 

 and the head of the piston. With such an instrument, 

 properly manipulated, the dose can always be controlled 

 with accuracv. 



