156 BACTERIOLOGY. 



is no tendency to penetrate through the opposite wall. 

 We never use a new hypodermatic needle until its point 

 is carefully ground down to a perfectly flat, slanting 

 surface and no more curvature exists. 



These differences may perhaps come out clearer if 

 represented diagrammatically. 



FIG. 24. 

 A 



In Fig. 24, A, the needle has the point usually seen 

 when new. 



In Fig. 24, B, the point has been ground down 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 employed for 

 subcutaneous injections. 



When the operation is to be performed, an assistant 

 holds the animal gently but firmly in the crouching 

 position upon a table. If the animal does not remain 

 quiet it is best to wrap it in a towel so that nothing but 

 its head protrudes, though in the most cases we have 

 not found this necessary, and particularly if the animal 

 has not been excited prior to the beginning of the 

 operation. 



The animal should be placed so that the ear upon 



