THE RELATION OF DIET TO DISEASE 445 
animals the disease is rare. Dogs are most frequently 
affected (about 1 in 12,000 deaths). It has also been 
described in horses, cattle and monkeys. In our records 
there was one case an Artie fox {Canis lagopus) present- 
ing a typical picture. Degeneration of the islands of 
Langerhans was seen in three other animals, but there 
was no other evidence of diabetes. This disease is not 
due to diet but to the absence of a normal ferment (pan- 
creaticozTj^mo-excitor) for one particular type of food. 
Irregularities of Fat Metabolism. 
Disorders of fat metabolism are very rare among 
lower animals notwithstanding the fact that fat even in 
the carnivorous diet, represents about 13 per cent, of the 
whole intake. It plays two important roles in the body, 
storage for energy reserve, and as a most essential 
structure in cellular protoplasm, in which position it joins 
with protein in complex combinations of still unknown 
composition which present to a striking degree the 
phenomenon of absorption. Very marked biological 
differences exist in the value of fats from different 
sources, due to the presence or absence of vitamines. 
The body fat is derived from the fat of the diet or is 
synthesized from glucose. The former is specific to the 
fat consumed while the latter is specific to the animal. In 
omnivores the type depends upon the vaiying extent to 
which animal fats enter the diet, in carnivores it depends 
almost entirely on the fat intake, while in the herbivores 
practically aU the fat is synthesized from the carbo- 
hydrate. On digestion, fat splits, yielding a glycerol and 
fatty acid which are collected in the lymph spaces of the 
intestinal mucosa, there changing to some complex com- 
bination which is not only soluble but diffusible. 
Fatty infiltration and fatty degeneration are condi- 
tions of much pathological interest and of great frequency 
in captive animals. The researches of Mansfield (31) have 
(31) Pfliiger's Arch., 1909 (129), 63. 
