INJECTION INTO THE CIRCULATION. 203 



in the other, leaving the area occupied by the pectoral 

 muscles, over which the inoculation is to be made, free 

 for manipulation. The hair should be closely cut with 

 the scissors in the case of the guinea-pigs and rabbits, 

 and the feathers pulled out in the case of the pigeon. 



INJECTION INTO THE CIRCULATION. It is not in- 

 frequently desirable to inject the material under consider- 

 ation directly into the circulation of an animal. If the 

 rabbit is to be employed for the purpose, the operation 

 is usually done upon one of the veins in the ear. 



To those who have had no practice in this procedure 

 it offers a great mauy difficulties ; but if the directions 

 which will be given are strictly observed, the greatest 

 of these obstacles to the successful performance of the 

 operations may be overcome. 



When viewing the circulation in the ear of the rabbit 

 by transmitted light, three conspicuous branches of the 

 main vessel (vena aurieularis posterior) will be seen. 

 One runs about centrally in the long axis of the ear, 

 one runs along its anterior margin, and one along its 

 posterior margin. The central branch (ramus anterior 

 of the vena aurieularis posterior) is the largest and 

 most conspicuous vessel of the ear, and is, therefore, 

 selected by the inexperienced as the branch into which 

 it would appear easiest to insert a hypodermic needle. 

 This, however, is fallacious. This vessel lies very loosely 

 imbedded in connective tissue, and in efforts to intro- 

 duce a needle into it, rolls about to such an extent that 

 only after a great deal of difficulty does the experiment 

 succeed. On the other hand, the posterior branch 

 (ramus lateralis posterior of the vena aurieularis poste- 

 rior) is a very fine, delicate vessel which runs along the 

 posterior margin of the ear, and which is so firmly fixed 



