EXPERIMENTS UPON ANIMALS. 97 
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 
Fig. 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 boen 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 
Fig. 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 voung 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. 
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