216 BACTERIOLOGY. 



tiated, however, by continuing the injection, when the 

 circulation of clear fluid through the vessels will not 

 only fail to take the place of the circulating blood, but 

 there will at the same time appear a localized swelling 

 under the skin about the point of the needle. The 

 needle must then be withdrawn and inserted into the 

 vessel at a point a little nearer to its proximal end. 



Care must be taken that no air is injected. 



The hypodermic syringe and needle must, previous 

 to operation, have been carefully sterilized in the steam 

 sterilizer or in boiling water. The animal must be 

 kept under close observation for about an hour after 

 injection. 



The operation is one that cannot be learned from 

 verbal description. It can only be successfully per- 

 formed after actual practice. 



If the precautions which have been mentioned are 

 observed, but little difficulty in performing the opera- 

 tion will be experienced. 



Its greater convenience and simplicity as compared 

 with other methods for the introduction of substances 

 into the circulation commend it as an operation with 

 which to make one's self familiar. The animals sustain 

 practically no wound, they experience no pain — at least 

 they give no evidence of pain — and no ansesthetic is 

 required. 



The form of syringe best suited for this operation is 

 of the ordinary design, but one that permits of thorough 

 sterilization by steam. It should be made of glass and 

 metal, with packings that may be sterilized by steam 

 without injury. The syringes commonly employed are 

 those shown in Fig. 47 — A, Koch's; B, Strohschein's; 

 Q, Overlack's. 



