446 DISEASE IN WILD MAMMALS AND BIRDS 
thrown considerable light upon these conditions. He 
found that the total fat content in cases of most marked 
degeneration was normal or reduced. The proportion of 
fat free from protein was increased and the firmly bound 
fat decreased. This increase is due to neutral fat brought 
from without the organ by the blood when for any cause 
the oxidative powers are decreased, and setting free of 
the previously invisible intercellular fat and lipoids, 
which are normally present in the cells, by autolytic or 
physicochemical changes. This condition is pretty evenly 
distributed among the dietary groups, the liver being 
most commonly involved. The hepatic cells are easily 
degenerated by the toxins or other harmful substances 
passing through the organ and become passive and unable 
to throw off or to utilize the deposited fat. In all prob- 
ability the same general situation occurs in the 
atheromatous changes in arteriosclerosis which on this 
diet shows a high incidence. The causative agent is prob- 
ably some poisonous substance, possibly a protein 
degradation product, indol, pressor substance, acting on 
the intima over long periods, or at irregular but often 
repeated periods causing first destruction then fat accu- 
mulation. It is also possible that it may be caused by 
repeated absorption of some sensitizing protein. 
Arteriosclerosis in these animals is often closely asso- 
ciated with nephritis. 
Obesity may result from excessive ingestion of food 
in individuals whose habits are sedentary and whose 
digestions are active or it may come from an inherent 
abnormality of metabolism dependent upon ductless 
gland disease. It is very common in castrated animals. 
The obesity of overeating is always of milder type than 
that associated with endocrine disturbance. 
So far as is knowTi there are two main disorders of fat 
metabolism — the failure of the diabetic to form fat from 
glucose, and acidosis, the inability of the organism to burn 
fat beyond betaoxybutyric acid, acetoacetic acid, or ace- 
