EXPERIMENTATION UPON ANIMALS. 159

of Meyer and Roux resemble ordinary hypodermic
syringes; that of Koch is supposed to possess the decided
advantage of not having a piston to come into contact
with the fluid to be injected. This is, however, some-
what disadvantageous inasmuch as the cushion of com-
pressed air that drives out the contents is elastic, and un-
less carefully watched will follow the injection into the
body of the animal. In making subcutaneous injections
there is no disadvantage or danger from the entrance of

FlG. 40.—I, Roux's bacteriological syringe; 2, Koch's syringe; 3, Meyer's
bacteriological syringe.

air beneath, the skin, but in intravenous injections it is
commonly supposed to be dangerous.

All syringes should be disinfected with carbolic acid
solutions before and after using, the carbolic acid being
allowed to act for some time and then washed out
with sterile water. Syringes should not be boiled, as
'it ruins the packings, whether of asbestos, leather, or
rubber.

The intravenous injections differ only in that the needle
of the syringe is introduced into a vein. This is easy in a
large animal like a horse, but is very difficult in a small
animal, and wellnigh impossible in anything smaller than
a rabbit. Such injections when given to rabbits are gen-
erally made into the ear-veins, as those most conspicuous
and accessible (Fig. 41). A peculiar and important fact
to remember is, that the less conspicuous posterior vein