SECTION XVII 
THE COMMUNICABLE DISEASES— PART I 
Tuberculosis. 
Nearly all infectious diseases have either a limited 
natural zoological distribution or are encountered chiefly 
in one order or division. Thus typhoid fever is peculiar 
to man, hog cholera to swine, foot-and-mouth disease to 
cows. A second group, including for example anthrax, 
variola, hemorrhagic septicemia and malignant edema, is 
somewhat less specific, and may occur in several varieties. 
There is no more widespread, important infection, 
zoologically, economically and hygienically, than tubercu- 
losis, and it would seem that all kinds of vertebrates are 
subject to it. Its manifestations too, are sufficiently 
similar to support the idea ihat there must have been 
originally a common ancestor of the viruses which we now 
designate separately by a term to indicate their immediate 
source (human, avian, etc.), and moreover it has been 
shown that any of the artificially separated varieties or 
subspecies may under certain circumstances infect all 
zoological families. 
There is, however, a varying resistance to the tubercle 
bacillus, certain zoological groups standing out preemi- 
nently as more or less susceptible to it. There is also a 
tendency for each animal group to present features more 
or less peculiar to itself, but nevertheless the character- 
istics, both gross and minute, of the disease caused by the 
Bacillus tuberculosis are sufficiently similar to permit 
close analogy and to establish a diagnosis when the bac- 
teria are found. 
The data collected at this Garden are well suited to 
elucidate the susceptibility of wild animals under captive 
conditions and to illustrate the nature of lesions in them. 
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