14 FOREWORD 
phia Garden by the European brown bear wliich in one 
year gave birth on January 16th, and in the following 
year on July 25th. It is another evidence of the profound 
effect of captivity on the captive animal. I know of no 
observations of the effect of captivity on the period 
of gestation. 
There is considerable mortality among captive 
animals from killing of cage-mates. I do not refer to 
sexual killing, already mentioned, or to fights over a 
female. Often males, with no females near, cannot be 
kept together ; probably sexual jealousy is at the bottom 
of it. Antelope and deer are especially inclined to scrap. 
Even a large enclosure \\dll not save the weaker male ; the 
stronger follows him with horrible persistency, some- 
times for days, around and around the enclosure, often 
at a walk, but always on the offensive, at least during the 
day ; until, careless from weariness, the weaker is caught 
unawares and finished by a horn-thrust in the side. 
Both birds and mammals often kill their mates when 
the mate is sick, or " down " from injury or disease. All 
animals hate sickness and death, and show their dislike 
by attacking or shunning it. Birds may get on happily 
together for months until one becomes sick, and as he 
crouches in a corner with ruffled feathers the others pick 
on him and finish him. The same is true of manmials, the 
sick one being horned or tramped to death by the mate 
with whom he had formerly been on most friendly terms. 
The keeper often reports an animal ''killed by its mate," 
whereas the mate has only given the coup de grace. 
This brutality is not universal. Rarely a parrakeet 
will stand guard over his sick and dying mate; and we 
have seen a ratel — of a ferocious family — stand guard 
over and resist the removal of his sick companion. 
The diagnosis of disease in wild animals is unsatis- 
factory ; usually impossible ; clinical study as we know it 
in the human is impossible. We know that the animal is 
sick, but not why. A certain group of symptoms accom- 
