EXPERIMENTS UPON ANIMALS. 



95 



Inoculations are made directly into the circulation through a 

 vein, into the subcutaneous connective tissue, or into one of the 

 serous cavities usually the peritoneal. 



The ordinary hypodermic syringe may be used in making injec- 

 tions, but this is difficult to sterilize on account of the leather piston, 

 and complications are liable to arise from its use which it is best to 

 avoid. The best way to sterilize a piston syringe is to wash it thor- 

 oughly with a solution of bichloride of mercury of 1 : 1,000, and then 

 to remove every trace of bichloride by washing in alcohol. But one 

 never feels quite sure that the most careful washing will insure steril- 

 ization, and it is best to use a syringe which may be sterilized by 



Fia. 71. 



heat, such as that of Koch, shown in Fig. 71. In this the metal point 

 and glass tube are easily sterilized in a hot-air oven. Fluid is drawn 

 into the syringe and forced out of it by a rubber ball which has a 

 perforation to be covered by the finger. 



The writer has for some years been in the habit of making injec- 

 tions in animals with an improvised glass syringe. This is made 

 from a piece of glass tubing in the same form as the collecting tubes 

 heretofore described. A bulb is blown at one end of the tube, and 

 the other end is drawn out to form a slender tube which serves as the 



Fm. 72. 



needle of the syringe (Fig. 72). By gently heating the bulb in an 

 alcohol lamp and immersing the open end of the capillary tube in 

 the fluid to be injected, this rises into the syringe as the expanded air 

 cools. Having introduced the glass point beneath the skin or into 

 the cavity of the abdomen of the animal to be injected, the contents 

 of the tube are forced out by again heating the bulb by means of a 

 small alcohol lamp. The glass point is easily forced through the 

 thin skin of a mouse or of a young rabbit ; but for animals with a 

 thicker skin it is necessary to cut through, or nearly through, the 

 skin with some other instrument. A small pair of curved scissors 

 answers very well for this purpose. 



