INJECTION INTO THE CIRCULATION. 155 



in the dense tissues which surround it that it is prevented 

 from rolling about under the point of the needle. The 

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

 nearer we approach its capillary extremity — ^the more 

 favorable become the conditions for the success of the 

 operation. 



Select, then, the very delicate vessel lying quite close 

 to the posterior margin of the ear, and make the injec- 

 tion as near to the apex of the ear as possible. The 

 injection is always to be made from the dorsal surface of 

 the ear. 



Of no less importance than the selection of the proper • 

 vessel, is the shape of the point of the needle employed. 



The hypodermatic needles as they come from the 

 makers are not suited at all for this operation be- 

 cause of the way in which their points are ground. 

 If one examines carefully the point of a new hypo- 

 dermatic needle it will be seen that the long point, in- 

 stead of presenting a flat, slanting surface, when viewed 

 from the side, is more or less of a curved surface. 

 Now, in efforts to introduce such a needle into vessel a 

 of very small calibre, it is commonly seen that the ex- 

 treme point of the needle, instead of remaining in the 

 vessel as it would do were it straight, very commonly 

 projects into the opposite wall, and as the needle is in- 

 serted further and further into the tissues, it is usually 

 pushed through the vessels into the loose tissues beyond, 

 and the material to be injected is deposited into these 

 tissues instead of into the circulation. If, on the con- 

 trary, the slanting poiat of the needle is ground down 

 until its surface is perfectly flat, and when viewed from 

 the side no more curvature exists, then when once in- 

 serted into a vessel it usually remains there, and there 



