418 DISEASE IN WILD MAMMALS AND BIRDS 
Either a highly developed concentrated glandular appa- 
ratus is added to the stomach, as in the wombats, beavers 
and dormice, or the stomach is subdivided, sacculated, or 
otherwise amplified as in the ruminants and herbivorous 
marsupials. Sometimes both complexities are combined 
as in the case of the sloths. If the simple stomach is 
retained, it is supplemented by a large sacculated colon or 
cecum, as in the horse. In birds, the proventricle is larger 
in meat- and fish-eaters, while the gizzard is more muscu- 
lar in grain- and insect-feeders, and the intestines are 
longer in those devouring coarse green grass and leaves. 
The length of the ceca is related entirely to the diet, the 
long ones corresponding to the diet which needs pro- 
tracted periods of time to exhaust its nutriment. 
The Bacterial Flora. 
The bacterial flora harbored in the intestinal tract is 
closely related to the type of food and to the character of 
the alimentary tract. Levin (2) found sterile intestinal 
tracts in white bears, seals, reindeer, eider ducks and 
penguins when in the Arctic regions; but these same 
animals when they are brought to a temperate climate 
rapidly acquire intestinal bacteria. The function of the 
normal inhabitants of the tract is, probably, to protect 
the body against invasions of obnoxious species. Herter 
found in man that a few species adapt themselves to the 
digestive tract and control the growth of new-comers 
capable of doing injury. These common varieties become 
a source of danger only when present in large numbers. 
Bacteria which produce decomposition of food in the 
digestive tract are of three types : (1) Pure putrefactive 
anaerobes, (2) organisms both fermentative and putre- 
factive, but tending generally to antagonize the putrefac- 
tive anaerobes, and (3) fermentative organisms. In the 
stomach, fermentation of carbohydrates with the 
(2) Ann. Inst. Past., 1899, XIII, 558, and Skandinavisches Arch. f. 
Physiol., 1904, XVI, 249. 
