212 BACTERIOLOGY. 



area the feathers should be plucked in the case of the 

 pigeon. 



Injection into the Circulation. — It is not in- 

 frequently desirable to inject the material under consid- 

 eration directly into the circulation of an animal. If 

 a rabbit is to be employed for the purpose, the opera- 

 tion 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 many dijfficulties; 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 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 posterior) is a 

 very fine, delicate vessel which runs along the posterior 

 margin of the ear, and whicli is so firmly fixed in the 

 dense tissues which surround it that it is prevented from 

 rolling about under the point of the needle. The fur- 

 ther away from the mouth of the vessel — that is, the 



