INJECTION INTO THE CIRCULATION. 191 



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 nothing but 

 its head protrudes, though in the most cases we have 

 not found this necessary, and particularly if the animal 

 has not been excited prior to the beginning of the 

 operation. 



The animal should be placed so that the ear upon 

 which the operation is to be performed 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 point at 

 M'hich the injection is to be made is to be shaved clean 

 of hair, by means of a razor and soap. 



The filled hypodermatic 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 

 coonective tissue. As soon as one thinks 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 quickly alter in appearance. 

 Instead of their containing blood, the colorless fluid 

 which is being injected will now be seen to circulate. 

 This must be carefully observed, for sometimes when the 

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

 lymph-spaces surrounding it, an appearance somewhat 

 similar is to be seen. It may always be differentiated, 



