224 BACTERIOLOGY 



employed by physicians for subcutaneous injections in 

 human beings. 



When the operation is to be performed an assistant holds 

 the animal gently but firmly in the crouching position upon 

 a table. If the animal does not remain quiet, it is best to 

 wrap it in a towel, so that only its head protrudes; though 

 in most cases we have not found this necessary, particularly 

 if the animal has not been excited prior to beginning the 

 operation. 



The ear in which the injection is to be made should be 

 shaved clean of hair by means of a razor and soap and then 

 washed with water. It is unnecessary to attempt disin- 

 fection of the skin. 



The animal should be placed so that the prepared ear 

 comes between the operator and the source of light. This 

 renders visible by transmitted light not only the coarser 

 vessels of the ear, but also their finer branches. 



The filled hypodermic syringe is taken in one hand and 

 with the other hand the ear is held firmly. The point of the 

 needle is then inserted through the skin and into the finest 

 part of the ramus posterior, the part nearest the apex of the 

 ear, where the course of the vessel is nearly straight. When 

 the point of the needle is in this vessel it gives to the hand 

 a sensation quite different from that felt when it is in the 

 midst of connective tissue. As soon as one supposes the 

 point of the needle is in the vessel a drop or two of the fluid 

 may be injected from the syringe, and, if his suspicions 

 are correct, the circulation in the small ramifications and 

 their anastomoses will rapidly alter in appearance — i. e., 

 the circulating blood will be displaced very quickly by the 

 clear, transparent fluid that is being injected. At this stage 

 one must proceed very carefully, for sometimes when the 



