144, Prof. LeConte on the Correlation of Forces. 
only possible but certain, on the principle of conservation of 
force, that decomposition of animal tissues should set free a 
force, a part of which is consumed in the recomposition of a 
larger amount of new matter and thus maintaining growth, a 
part in animal heat, and a part in animal activity of all sorts. 
In this view of the case, we see at once the absolute necessity 
that the food of animals should be organized. Upon the prin- 
ciple of conservation of force, growth and animal activity—in a 
word, animal life—would otherwise be impossible. 
It follows also from the above, that the higher the organiza- 
tion of the food, the smaller the amount of force necessary to 
effect assimilation, and therefore the larger the amount of resi- 
dual force to be expended in animal heat and animal activity. 
In this we find a ready explanation of the superior activity of 
carnivorous animals, and the loss of animal activity which results 
in a state of domestication from the use of vegetable diet ; also 
of the supposed superior activity of men fed upon meat diet. 
10th. I have spoken thus far of only one source of vital 
force in animals, viz. the decomposition of the tissues. I have 
attempted to show how, upon, the principle of conservation 
of force, this is sufficient to carry on the growth and the activity 
of the animal organism. But decomposition of the tissues, 
though the fundamental source—the source characteristic of, and 
peculiar to animals—of immediate and universal necessity in this 
kingdom, and in many cases sufficient of itself, is not the only 
source. There is also in animals, as in plants, a supplemental 
source, viz. the decomposition of food. 
It is well known that the food of animals consists of two kinds, 
the nitrogenous, such as albumen, fibrine, caseine, &c.; and the 
non-nitrogenous, such as fat, starch, sugar, gum, &c. According 
to all physiologists since Liebig, the nitrogenous alone are used 
in the repair and growth of the tissues. The non-nitrogenous 
are either quickly consumed in respiration, or else are laid up in 
the form of fat for future consumption in the same way. Now 
there can be no doubt that animals may live entirely on nitro- 
genous food; in which case the whole vital force, whether for 
assimilation of food or for animal heat and animal activity, is 
derived from the decomposition of the tissues. This is the case 
also, apparently, in the starving animal, particularly if lean. But 
in almost all cases much food in the form of fat, starch, sugar, 
&c. (non-nitrogenous),'is never transformed at all into tissues, 
but is taken into the blood, gradually decomposed, oxidized in 
the course of the circulation, changed into CO? and HO, and 
finally removed by exhalation from the lungs. Now what is 
the object of the non-nitrogenous food, since these do not form 
any part of the tissues, but are again decomposed and thrown 
