INJECTION INTO THE CIRCULATION. 213 



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. From 

 time to time the vessels of the ear will be found to con- 

 tain so little blood that they are hardly distinguishable, 

 making it very difficult to introduce the needle. This 

 is sometimes overcome by pressure at the root of the 

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

 of the vessels. A very satisfactory method of causing 

 the veins to become more prominent is to lightly press 

 or gently prick 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 dilated, dis- 

 tended with blood, readily distinguished from the sur- 

 rounding tissues, and may then be easily punctured by 

 the needle of the syringe. 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 way 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 pre- 

 senting a flatj slanting surface when viewed from the 

 side, has a more or less curved surface. Now, in efforts 

 to introduce such a needle into a vessel of very small 

 calibre, it is commonly seen that the extreme point of 

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

 would do were it straight, very commonly projects into 



10* 



