DIFFERENT KINDS OF FOOD. 7 
Dr. Pereira states the following arguments, and the comments 
on them: — 
The first argument is, that as the animal tissues contain nitro- 
gen as one of their essential constituents, and as this element 
cannot be created in the system, it must be derived from either 
the food or the atmosphere ; but as it is not absorbed from the 
atmosphere in the vital process, it must be obtained from the food. 
He quotes a number of authors to prove that during respiration 
nitrogen is both absorbed and exhaled by the blood or lungs. 
Liebig asserts that “ no nitrogen is absorbed from the atmo- 
sphere/’ yet admits of ammonia in the air. If nitrogen be not 
absorbed, the tissues can only obtain this element from food. 
The second argument is, that non-nitrogenized foods alone are 
incapable of supporting animal life. 
Gum, sugar, starch, or butter alone, cannot preserve the life of 
animals; as dogs fed exclusively on sugar and water, or butter 
and gum, died from thirty-one to thirty-four days. Geese fed on 
sugar and water, or gum and water, or starch and water, died 
from seventeen to twenty-four days : yet a lady refused to take 
any other nourishment whatever during several years than lump 
sugar : that people fed on potatoes require milk : that a diet of 
one nitrogenized principle exclusively is incapable of supporting 
animal life. Fibrine, albumen, or gelatine, taken separately, does 
not support life ; even the artificial mixture of these principles 
is insufficient to preserve life — for dogs thus fed ultimately died 
with all the signs of complete inanition ; while, on the other hand, 
a diet of muscular flesh, or of raw bones, or of gluten exclusively, 
is capable of complete and prolonged nutrition. 
The third argument is, that the food of all animals, herbivor- 
ous and carnivorous, contains nitrogenized matters, identical in 
composition with the principal constituents of the blood and or- 
ganized tissues of the animal body ; and, therefore, the carbon of 
gum, sugar, and starch, and the carbon and hydrogen of the fats 
and oils, are not required for the production of blood. 
Vegetables contain organic principles identical in composition 
with animal fibrine, albumen, and caseine. Liebig observes, 
“ that they have the same proportion of carbon, hydrogen, oxy- 
gen, and nitrogen, which the animal principles contain, but also 
in possessing the same relative amount of sulphur, phosphorus, 
and phosphate of lime.” 
The fourth argument is, that the quantity of nitrogenized food 
which herbivorous animals consume is amply sufficient for the 
growth and development of their organs, and for the supply of 
waste. 
M. Boussingault demonstrates the truth of this statement in 
the case of the horse. 
