6 FOREWORD 
medium size as in very large ones. A deer or antelope in 
a large enclosure does not use all its domain. It usually 
has a favorite corner near the food, water and shelter, 
and stays there. Nor has a large enclosure been found 
perceptibly to diminish mortality from cage-mates. The 
stronger will follow the weaker until he gets him, no 
matter what the enclosure. Even in the large flying cage 
for birds it is necessary to keep out those of a scrappy 
disposition. From the point of view of the public small 
enclosures are more satisfactory. 
Mental disease in captive animals offers a fasci- 
nating field for study — now chiefly speculative. Many 
conditions are present to produce it — all the con- 
ditions that cause prison psychoses in man. And 
many if not all the insane and perverted acts 
of animals have their counterpart in the human. 
Masturbation is ver>' common in mammals. Eating of 
their own feces, coprophagy, is not infrequent, and is 
especially notable in one of the highest types — the Chim- 
panzee. Perhaps occasionally coprophagy may be due to 
some defect in diet. There is no instinctive disgust at 
excrement in the lower animals any more than there is in 
the uneducated child. Nevertheless, eating feces cannot 
be healthful, and probably does not occur in nature ; and 
occurs only in the human with mental disease. 
Some of the insane acts of animals if prevalent in the 
wild would probably cause the extinction of the race. 
Such are killing of the 3'oung by the father and by the 
mother ; killing of the female by the male, usually during 
rutting time, in some instances reminding one of Sadism 
in man. This kind of sexual killing does not often occur 
in the wild. The female has a better chance to escape, 
and the male probably does not feel so inclined to damage 
her when he chooses her himself as when she is chosen for 
him by his gaoler. When the mother devours her young 
it is usually shortly after birth. I have, however, the 
record of a Jungle cat {Felis chaus) who ate two of her 
