THE 
AMERICAN NATURALIST. 
VOL. ZIT JANUARY, 1887. Mo; T: 
* 
PARASITIC BACTERIA AND THEIR RELATION 
TO SAPROPHYTES.': 
BY THEOBALD SMITH, 
pee Basie. whether they be animal or vegetable, have cer- 
tain characters in common which are due to their relation 
to their host rather than to their own intrinsic organization. I 
shall endeavor to point out a few of those which may be ob- 
served among bacteria parasitic on animals. Since they usually 
give rise to well-defined diseases, they are also called pathogenic 
bacteria, or more popularly, disease-germs. Almost all patho- 
genic forms may be considered true parasites, at the same time 
all truly parasitic forms have been found pathogenic. 
There are certain external regions of the animal body quite 
uniformly the seat of specific bacteria. They are the skin and 
alimentary canal. Observations have shown that in the different 
Sections of the digestive tract different bacteria are found. To 
some of these a digestive function has been attributed, the power 
of peptonizing albumens, and thus facilitating their absorption. 
The bacteria inhabiting the mouth are numerous, and some are 
found quite constantly, such as the well-known Leptothrix buccalis. 
A microcobe has also been found which some years ago was 
€rroneously regarded as identical with the cholera bacillus. The 
mistake was pointed out by demonstrating its inability to grow 
upon gelatine, which the cholera germ readily does. I have re- 
peatedly found in my own saliva the same liquefying coccus- 
oo ae C., December 11, 1886. 
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