INTRODUCTION 25 
cannot be estimated by the examples seen in menageries. 
Judging by the accounts of collectors and hunters and 
upon the more reliable of the moving picture displays of 
wild animals in their native haunts, it would seem prob- 
able that under normal conditions of habitat the average 
size of wild beasts is considerably in excess of that in 
park specimens. 
The effect of captivity may also be felt in the direction 
of reduced resistance to infectious diseases. Brooks, of 
the New York Park, expresses the view that captivity 
increases susceptibility to bacteria and causes paren- 
chymatous degenerations. In the latter direction it is 
interesting to learn that Seligman of London claims to 
have seen sudden deaths in wading and struthious birds 
from myocardial disease, without valvular or other 
lesions, for which he holds the enervating effects of cap- 
tivity responsible. It is well recognized that a species 
may be unusually susceptible to a disease that it has not 
encountered in its phylogenic development. Man illus- 
trates this peculiarity very clearly. Europeans were 
found exceedingly susceptible to sleeping sickness when 
they went first to the part of Africa inhabited by the tsetse 
fly, and the American Indians died in hordes when they 
met the tubercle bacillus for the first time. Judging by 
the ravages of tuberculosis in captive monkeys a similar 
susceptibility probably explains the matter for there are 
no entirely satisfactory records of this disease among 
them in the wild state. 
In so far as general susceptibility to infection is con- 
cerned, it may be in part due to one of the artificial 
conditions of captivity, that of inbreeding. This influence 
is undoubtedly very great, both by chance in families, and 
by intention on the part of dealers as well as the mating 
which occurs in menageries. However, it is not known 
how far inbreeding may go in the wild state so that one 
must be very careful about drawing conclusions in this 
particular. Several years ago, at the time we reported 
3 
