226 



BACTERIOLOGY 



For operations requiring exact dosage experience has led 

 me to prefer a syringe after the pattern of C, in Fig. 45 — i. e., 

 the form commonly used by physicians. The reason for 

 this is as follows: in making injections, either into the cir- 

 culation or under the skin, there is a certain amount of 

 resistance to the passage of fluid from the needle. If one 

 overcomes this resistance by means of a cushion of com- 

 pressed air, as is the case in syringes A and B, Fig. 45, the 

 sudden expansion of the air in the body of the syringe when 



Fig. 45 



Forms of hypodermic syringe. A, Koch's syringe; B, syringe of Strohschein ; 

 C, Overlack's form. 



resistance is overcome frequently causes a larger amount 

 of fluid to be injected 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 a:n instrument, properly manipulated, the dose 

 can always be controlled with accuracy. 



Inoculation into the Lymphatic Circulation. — Fluid cultures 

 or suspensions of bacteria may be injected into the lym- 



