38 DISEASE IN WILD MAMMALS AND BIRDS 
by a rather firm air sac wall, makes it difficult for these 
organs to expand and therefore renders even a simple 
congestion a dangerous thing. The position of the ovary- 
subjects the shell-less egg to much danger from the 
intestinal area. 
These and many other peculiarities of anatomy 
affect the pathological picture in birds. To be sure 
there are also noteworthy differences among the Mam- 
malia, notably in the intestinal and genital tracts, 
but the pathologic response is not so varied as in the 
birds. "WTien due allowance is made for the kind of 
stomach and absorptive area, apparent differences can 
be reconciled. For example, there is little confusion 
experienced in comparing acute erosive gastritis or the 
follicular enteritis of an omnivorous intestinal tract (man 
or pig), of a sacculated stomach and absorptive tract (the 
marsupial), of a carnivorous gut (cat) or a herbivorous 
compound stomach vrith. its long digestive and water- 
absorbing surface (cow or camel) and an expansive 
muscular organ with a very extensive digestive area 
(seal). The type of lesion seems the same, in that inflam- 
mation, pus, necrosis, granulation tissue and cicatrices 
are comparable throughout the series. The size of the 
hind gut has been taken by Metchnikoff as an indicator of 
the possibility of intoxication by degradation products of 
digestion. He believes that the capacious colon of herbiv- 
ora and the short small one in carnivora explain the 
relatively greater life in the latter, because here less 
stagnation and absorption can take place. A reference to 
the expected lengths of life given before hardly substan- 
tiates this, and in our later chapters there will be found 
no strong indication that animals with large colons suffer 
with degenerative visceral changes more than those mth 
small ones ; nay even the reverse may be found true. 
In regard to epizootics the behavior of man and lower 
animals is similar except perhaps that during an outbreak 
a smaller percentage of the latter give evidence of indi- 
