218 BACTERIOLOGY. 



margin of the car, and 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 

 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. 



After shaving the ear and carefully washing it with 

 clean water select the very delicate vessel lying quite 

 close to the posterior margin of the ear, and make the 

 injection as near to the apex of the ear as possible. At 

 times the vessels of the ear will be found to contain 

 so little blood that they are hardly distinguishable, 

 making it very difficult to introduce the needle into 

 them. This is sometimes overcome by pressure at the 

 root of the ear, causing stasis of the blood and distention 

 of the vessels. A very satisfactory method of causing 

 the veins to become prominent is to press lightly or 

 prick gently with the point of a needle the skin over 

 the vessel to be used. In a few seconds, as a result of 

 this irritation, the vessel will have become distended 

 with blood, and readily distinguishable from the sur- 

 rounding tissue; it may then be easily punctured by 

 the needle of the syringe. A sharp flick with the 

 finger will often produce the same result. 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 hypodermic needles as they come from the 

 makers are not suited at all for this operation, because 

 of the manner in which their points are ground. If 

 one examine carefully the point of a new hypodermic 

 needle, it will be seen that the long point, instead of 



