SUBCUTANEOUS INOCULATION OF ANIMALS 225 



needle-point is not actually in the vessel, but is in the lymph- 

 spaces surrounding it, an appearance somewhat similar is 

 seen. This may always be differentiated, however, by con- 

 tinuing the injection, when the flow of clear fluid through 

 the vessels will not only fail to take the place of the cir- 

 culating blood, but at the same time a localized swelling, 

 due to an accumulation 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 must then be withdrawn and inserted into the vessel at a 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 steri- 

 lizer 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 performed after 

 actual practice. If the precautions which have been men- 

 tioned 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 suffering — at least they give 

 no evidence of pain — and no anesthetic 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. 

 15 



