LIEBIG ON THE AZOTIZED PRINCIPLES OF PLANTS, 245 
the azotized portions of their bodies take their rise. It is in the 
vegetable kingdom that the nourishment of animals in general 
is prepared ; for, strictly speaking, carnivorous animals, when 
they consume other animals which have fed on vegetables, con- 
sume only those vegetable principles which have served the 
latter as nourishment. Every azotized animal substance has con- 
sequently its origin in plants. 
It is well known that carnivorous and graminivorous animals 
have very different digestive organs, but that the assimilation is 
performed in both by the blood ; the comparison becomes there- 
fore a most important subject for the physiologist. 
In carnivorous animals the process of nutrition is very simple ; 
the nourishment they take is identically the same as the princi- 
pal component parts of their own bodies: the flesh, blood, mem- 
branes, &c. which they consume, are in no respect different, 
chemically speaking, from their own flesh and blood. The food 
of carnivorous animals assumes a new form in the stomach and 
organs of digestion, but its chemical composition suffers no 
change; it is made soluble, and therefore becomes transferable 
to the different parts of the body, taking again the form of blood 
from which it originated. In that class of animals the vital ac- 
tion of the organs in digestion and the formation of blood, is 
confined to a mere change of the condition of the nutritive 
matter, as it is all capable of assimilation in the state in which 
it is taken ; and such substances only pass unchanged through 
the alimentary canal, as the excess of inorganic substances in the 
food, and the earthy matter of the bones, with insoluble salts of 
Magnesia. The process of nutrition in graminivorous animals 
appears much more complicated ; their digestive organs are more 
complex, and their food has much less resemblance to the con- 
stituents of their bodies. 
All those parts of plants which serve as nourishment to gra- 
minivorous animals, contain, besides the azotized compounds 
named, certain others absolutely necessary for the support of life, 
which yet contain no nitrogen. These compounds, among which 
are sugar, amylin, and gum, are evidently applied to some par- 
ticular purpose, as they disappear in the organization ; they, no 
doubt, take a part in certain processes, which, in carnivorous 
animals, are conducted in a different manner. 
Before being able to decide with certainty as to the part in 
the vital processes of animals, performed by the substances desti- 
