176 PHYSIOLOGY OF THE BACTERIA. 
Bacteria in Liquids Exposed to the Air.—In 
order to comprehend the importance of bacteria 
from a surgical point of view, it is sufficient to put 
a drop of pus from an open wound under the micro- 
scope. In the majority of cases the presence of 
bacteria will be demonstrated. And, truly, there 
is nothing in this which should astonish us, if we 
remember what has been said above, since we 
know the facility with which these vegetables de- 
velop in all the liquids of the organism, and the 
resistance which they offer to all but the most 
powerful agents. However, all pus is not equally 
suitable for the development of these organisms. 
It is easy to remark that they are more abundant 
in pus of a bad character, in that which smells bad 
and exhales an odor of butyric acid. They are 
also more commonly found in pus which has re- 
mained a long time in wounds having hidden si- 
nuses. But while recognizing these differences, 
we must confess that there is nothing absolutely 
fixed about them, and above all that they do not 
bear a constant relation with the conditions which 
govern the genesis of putridity. 
It is certain, also, that the conditions surround- 
ing the sick person, the quality of the air in which 
his wound is bathed, are conditions which it is 
necessary to consider. And this results from 
what we have said relative to atmospheric germs. 
For example, when we submit to maceration in 
distilled water, dust gathered in a hospital, on one 
hand, and on the other, dust from a different lo- 
cality, taken in the country, for instance. The 
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