to (lie Rearing and Feeding of Catlle. 
217 
of this identity of vegetable albumen with flosli, is there any dif- 
ficiiltv in comprehending the nutrition of vegetable feeders. 
P/^h/.s, tlien, in reality form i\\c fesh of animals ; and the latter, 
merely appropriate it a place in their organism. 
A little consideration will show that this is a very wise arrange- 
ment of nature. The vitality of plants is not required to e.xecute 
the commands of volition, and therefore its whole powers are 
employed in creating new compounds ; but in animals the vital 
principle has many duties to perform, assigned to it by the will. 
Its powers are therefore husbanded for this end, and not expended 
in compelling the chemical forces to yield their usual athnities, 
for the production of particular constituents of the body, out of 
substances wholly dissimilar in composition. All, then, that the 
vitality in the animal economy has to perform connected with 
nutrition, is to assign a place and form to the food, which is al- 
ready of the proper composition. 
It is to Liebig that we owe the discovery of this important fact ; 
for the analyses now placed before you (with the e.xceplion of that 
by Boussingault) were executed at his request, in order to esta- 
blish the truth of his views. 
The food of herbivorous animals contains other compounds, 
such as starch, sugar, and gum. From these the element nitro- 
gen is absent, and hence they cannot of themselves form flesh. 
Indeed, in one sense, they cannot be considered as nutritious, for 
it is found that animals die when fed upon such food alone ; 
yet constituents of plants destitute of nitrogen occur in the food 
of all vegetable feeders. For what purpose, then, are they de- 
signed ? 
The average temperature of the bodies of our cattle is about 
100 degrees, or more than 40 degrees higher than the ordinary 
temperature of this climate. Hence there must be some provision 
in the animal body to sustain the heat, which is absolutely neces- 
sary for the performance of the organic functions. The air, being 
so much colder than the body, must constantly withdraw from it 
heat, and tend to lower its temperature. Whence, then, comes the 
fuel for the production of the heat ? 
The fuel consists of those ingredients of food from which nitro- 
gen is absent ; they all contain carbon and the elements of water. 
We know that oxygen is continually exhaled in the air we breathe, 
and that it is never again expired as such. Expired air consists of 
carbonic acid, a gas composed of carbon and oxygen. In the 
body therefore, the oxygen has united with carbon ; or it has pro- 
duced the very gas tvhich is obtained hy burning a piece of 
charcoal in the open air. Now the heat generated by the com- 
bustion of the carbon in the body must be exactly equivalent to 
that produced by burning the same amount in the atmosphere. 
