420 DISEASE IN WILD MAMMALS AND BIRDS 
The intestinal flora also changes along rather definite 
lines as the diet of the host changes from the monotony of 
the infant to the variety of the adult. At birth the tract 
is sterile, but bacteria soon make their entry through 
the mouth in food and water. The majority of these 
organisms pass to the stomach where many are destroyed, 
but a number travel to the intestines where they may gain 
a foothold. There is always a mechanical transportation 
of intestinal bacteria from higher to lower levels. A con- 
tinued preponderance of protein in the diet of all animals 
leads to a partial or complete suppression of the Gram- 
positive acid-forming groups and an increase of the pro- 
teolytic Gram-negative types ; while on the other hand an 
excess of carbohydrate leads to diminution or suppression 
of proteolytic activity and an increase in the fermentative 
organisms. Therefore the most important normal factor 
in determining the intestinal flora in health is the chem- 
ical composition of the ingested foods. 
The nature of the dominant organisms which develop 
in diets rich in carbohydrates varies \vith the carbo- 
hydrate itself. In all ordinary diets there are (1) starches 
— forms not readily fermentable, and (2) sugars — which 
are largely absorbed from the higher levels of the small 
intestine, lea\T.ng residual starches and proteins in 
relatively great concentration in the lower levels. There- 
fore the obligate fermentative organisms are prominent 
only in the higher levels, the facultative appear in the 
intermediate places, and the obligate proteolytic organ- 
isms in the lower intestines. This accounts in a measure 
for the great increase of lower intestinal disturbances in 
omnivores. Complete proteins resist putrefaction, but 
the products of protein digestion and of the intestinal 
secretions constitute the main substrata for putrefactive 
bacteria. Animal protein develops more active proteo- 
lytic bacteria than vegetable protein, which accounts for 
the greater predominance of putrefactive infections in 
carnivores than in omnivores. 
