THE RELATION OF DIET TO DISEASE 453 
prominent, far outstripping the incidence of this condi- 
tion in other classes. 
This diet yields a large and quickly available amount of 
carbohydrate which in conjunction with the moisture, heat 
and bacteria which are unavoidably associated mth raw 
vegetables, makes an ideal situation for infection. These 
foods carry many saprophytic bacteria, moulds, etc. In 
birds the conditions are aggravated by the injuries that 
may occur from the sharp objects picked up with the 
gravel. The incidence of acute infection is higher among 
birds than among mammals of this group, and often there 
is involvement of the whole tract. The explanation of the 
other pathological findings occurring among birds must 
be found in the frequently repeated low grade infections 
which result finally in the production of chronic lesions 
in the digestive tract, liver, pancreas and kidney. Toxins 
as an etiological factor cannot be altogether excluded, but 
as a rule they are not important because the by-products 
of vegetables are distinctly less toxic than those derived 
from animal sources. Arteriosclerosis is much less fre- 
quent and less intensive in herbivorous birds than among 
the carnivorous, probably because of differences in the 
concentration and character of toxins in the two groups. 
Soft Herbiv^orous Diet. 
The diet of succulent vegetables is composed of tubers, 
edible roots and leaves. The tubers and edible roots are 
high in water and carbohydrate and poor in the amount 
and quality of the protein, most of which is not even a true 
protein but a mixture of aminoacids. The leaves, on the 
contrary, are rich in organic ash, especially calcium, 
sodium, chlorine, and fat soluble A vitamine, and as a rule 
contain a good quality of protein. They often, however, 
contain injurious substances. This diet, while measurably 
less nutritious than that of the carnivores, can satisfac- 
torily nourish many animals with an extensive intestinal 
tract during growth and even throughout their entire life. 
