24 DISEASE IN WILD MAMMALS AND BIRDS 
I shall quote a case of an opossum wherein only one-tenth 
of the respirable surface seemed to have remained; we 
have repeatedly seen both lungs of a monkey apparently 
entirely solid. Such physical vital incompatibilities 
might be exemplified by many other cases, but when one 
reviews the physiological margin of safety, inexplicable 
and contradictory instances are equally numerous. 1 
have seen a male deer run a doe against the fence and 
butt her, without result, whereas in an apparently similar 
occurrence the animal would be dead in a short time. 
Numerous instances of slight enteritis of a short stretch 
of duodenum or ileum have killed, with almost nothing to 
be found microscopically, and on many occasions we have 
been chagrined in being unable to discover the cause of 
death. The capacity of self-healing is a variable one, but 
seems in direct proportion to the quietness and seclusion 
possible for the animal and inversely to the chance of 
bacterial infection. 
The effect of captivity has been the subject of much 
speculation. For the preservation of health it would seem 
that animals require periods of rest and activity, thor- 
ough elimination, possibly a moderate exercise of their 
procreative functions, but most of all, appropriate food 
obtained by the physical effort we term chase. All but 
the very last condition is supplied in a measure in well 
managed collections. The degenerating effect of the 
absence of chase must be admitted. An interesting and 
suggestive example of this was noted by Mr. Jones at the 
London Zoological Gardens. He observed the skull of a 
lion that had been in captivity thirteen years, in which the 
canine area of the face and the part of the skull acting as 
the insertion for the seizing and holding muscles had 
undergone atrophy while the chewing muscles with their 
bony bases had remained normal. Numerous examples 
of disease atrophy are on record and those of a 
physical nature must have counterparts in the realm 
of physiology. The size to which an animal will attain 
