SUBCUTANEOUS INOCULATION OF ANIMALS 221 



tissue under the skin over this part of the back in the way 

 that has just been described. It is always best to insert the 

 needle some distance along the spinal column, and thus 

 deposit the material as far from the surface-wound as 

 possible. 



Injection into the Circulation. — It is not infrequently 

 desirable to inject the material under consideration directly 

 into the circulation of an animal. If a rabbit is employed 

 for the purpose, the operation is usually done upon one of 

 the veins in the ear. To those who have had no practice 

 with this procedure it offers a great many difficulties; but 

 if the directions which will be given are strictly observed 

 the greatest of these obstacles to the successful performance 

 of the operation may be overcome. 



When viewing the circulation in the ear of the rabbit by 

 transmitted light three conspicuous branches of the main 

 vessel {vena auricularis 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 auricularis 

 posterior) is the largest and most conspicuous vessel of the 

 ear, and is, therefore, believed by the inexperienced to be 

 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 introduce 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 auricularis 

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

 posterior margin of the ear, and is so firmly fixed in the dense 

 tissues which surround it that it is prevented from rolling 



