890 The American Naturalist. [November, 
reconstructed through the agency of animal protoplasm. In no 
other way can the energy required in animal nutrition be 
obtained, and as an incident of the destructive metabolism of 
foods.in the process of digestion the materials for the construc- 
tive process are provided for immediate use in a simpler form 
than that in which they were ingested. - 
In general terms we may then say that the anabolic pro- 
cesses of animal nutrition consist in utilizing the liberated 
energy in building these disintegrated food constituents into 
protoplasm, with a storing of the energy as an essential condi- 
tion of its constitution; and the animal proteids and fats, and 
in fact the tissues generally are the katastates of its destructive 
metabolism, that contain less potential energy than the proto- 
plasm from which they are formed; the difference appearing 
as animal heat, which is supplemented by the destructive 
metabolism of the tissues involved in their functional activity, 
or what is popularly called the wear and tear of the system. 
As in plants, protoplasm is the summit, or highest phase of 
the anabolic activities, and tissue building must be looked 
upon as a result of its katabolic transformations. 
In the higher animals the nutritive processes are more com- 
plex, and the number of upward and downward steps of meta- 
bolism is increased through the elaboration of a common nutri- 
tive fluid, the blood; but the sum and final outcome of the 
anabolic and katabolic changes are essentially the same as in 
the simpler organisms. Energy is used and stored up in the 
anabolic or constructive processes, and liberated again as 
animal heat in the “simultaneous and successive” katabolic 
processes which result in the formation of the various tissues. 
Protoplasm is no longer looked upon asa substance of a 
definite chemical composition and constitution, as it must vary 
widely in its specific properties in the different species of 
plants and animals, and even in the different organs of the 
same animal, and the varieties of protoplasm are therefore 
innumerable. 
In addition to these variations arising from the character- 
istics of protoplasm in different species, and in their highly 
differentiated organs, the anastates representing the successive 
