98 EXPERIMENTS UPON ANIMALS, 
Generally, in making injections into animals, it is customary to 
remove the hair for some distance around the point of inoculation 
with scissors and razor, and then to sterilize the surface by careful 
washing with a solution of bichloride of mercury. This precaution 
is necessary in researches in which pathogenic bacteria are being 
tested, in order to remove any possibility of accidental inoculation 
with germs other than those under investigation, and, as a conse- 
quence, a mistaken inference as to the pathogenic action of the spe- 
cies under investigation. But when we know the specific pathogenic 
power of a certain microédrganism it is hardly necessary to take this 
precaution, as a few drops of culture will contain millions of the bac- 
teria, while contamination, if it occurs from the surface of the body, 
must be by a comparatively small number of bacteria, which are 
likely to be of a harmless kind which will have no influence on the 
result of the experiment. 
Instead of sterilizing the surface, the writer usually clips away a 
small portion of skin with curved scissors, not cutting deep enough 
to draw blood, but leaving a bare surface through which the point of 
the syringe can be iniroduced with very little danger of carrying bac- 
teria into the connective tissue other than those contained in the 
syringe. 
In making injections into the peidionaal cavity care must be taken 
not to wound the liver or the distended stomach. The intestine is 
not very likely to be wounded, as it slips out of the way. By seizing 
‘a longitudinal fold of the abdominal wall and pushing the point of 
the syringe quite through it, and then releasing the fold and care- 
fully withdrawing the instrument until the point remains in the 
cavity, the danger of wounding the intestine will be reduced to a 
minimum. 
Injections into the circulation are made by exposing a vein and 
carefully introducing the needle of the syringe in the direction of 
the blood current. Care must of course be taken not to inject air. 
In the rabbit one of the large veins of the ear may be conveniently 
penetrated by the point of a hypodermic syringe without any pre- 
vious dissection. The ear is first washed with a solution of bichloride 
of mercury or simply with warm water. The animal had better be 
carefully wrapped in a towel to control its movements. The veins 
are distended by compressing them near the base of the ear. When 
the point of the needle has not been properly introduced, and the 
fluid to be injected escapes in the surrounding connective tissue, it 
will commonly be best to withdraw the syringe and make the 
attempt upon another vein. As pointed out by Abbott, the needle 
of the syringe should be ground flat at the point, and not curved as 
is commonly the case. 
