INJECTION INTO THE CIRCULATION. 221 



sel, but is in the lymph-spaces surrounding it, an ap- 

 pearance somewhat similar is seen. This may always 

 be differentiated, however, by continuing the injection, 

 when the flow of clear fluid through the vessels will not 

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

 at the same time a localized swelling, due to an accu- 

 mulation of the fluid injected, will appear 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 then be withdrawn and inserted into the vessel at a 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 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 operation will be experienced. 



Its greater convenience and simplicity, as compared 

 with other methods for the introduction of substances 

 into the circulation, commend it as a technical procedure 

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

 sustain practically no wound, they experience no suffer- 

 ing at least they give no evidence of pain and no 

 anaesthetic 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. 45. 



For operations requiring exact dosage experience 



