SUBCUTANEOUS INOCULATION OF ANIMALS 223 



needle, instead of remaining in the vessel, as it would do 

 were it straight (or "chisel pointed"), very commonly pro- 

 jects into the opposite wall; and as the needle is inserted 

 further and further it is usually pushed through the vessel- 

 walls into the loose tissues beyond, and the material to be 

 injected is deposited in these tissues, instead of into the 

 circulation. If, on the contrary, the slanting point of the 

 needle be ground until its surface is perfectly flat when 

 viewed from the side, and no curvature exists, then when 

 once inserted it usually remains within the vessel, and there 



Fig. 44 

 o 



Hypodermic needles, magnified, u, improper point; 6, proper shape of 



point. 



is no tendency to penetrate the opposite wall. We never 

 use a new hypodermic needle until its point is carefully 

 ground to a perfectly flat, slanting surface with no curvature 

 whatever. 



These differences may perhaps be more easily understood 

 if represented diagrammatically. In Fig. 44, a, the needle 

 has the point usually seen when new. In Fig. 44, b, the 

 point has been ground to the shape best suited for this 

 operation. The needles need not be returned to the maker. 

 One Can grind them to the shape desired in a few minutes 

 upon an oilstone. The size of the needle is that commonly 



