. 1912] _ _PEIRCE—RESPIRATION FEY 
that the loss of heat by a warm-blooded animal is very great. 
When we reflect that all of the heat lost is liberated from the food 
of the animal, that the loss by radiation will vary with the tempera- 
ture of the environment and the efficiency of the animal’s covering 
as an insulator, whether this be hair, feathers, subcutaneous fat, 
or clothing, and that the loss by exhalation will also vary with the 
rate of exhalation, then we must realize that very much of the heat 
liberated in respiration is lost. What percentage this is in the case 
of a mouse I do not know, and it is hardly necessary to know at 
the moment. It is evident that if the liberation of heat is the 
essential result of respiration, respiration must be an excessively 
wasteful process. 
Having once conceived respiration to be primarily for furnishing 
the living organism with energy in the form of heat, I am con- 
strained now to regard it very differently. That it is the chief 
means of liberating energy still seems to me most probable; but 
apart from the production and maintenance of a body temperature 
apparently most favorable to the other functions collectively, the 
liberation of heat in respiration appears to be wasteful. It may be 
as useless as it is inevitable. 
The material products of respiration vary with the food, with 
the materials oxidized, directly or indirectly, in the body. Intra- 
cellular respiration, or the catabolic processes, the end products of 
which are oxides and heat, may not only produce within the cell 
the optimum temperature for its activities and liberate energy at 
once converted into work, but they may also neutralize (destroy) 
substances which would otherwise be or become injurious to it. 
The oxidation of these substances would necessarily be accompanied 
by heat liberation. The heat thus liberated must be either con- 
verted into work or given off, lest again the organism suffer. We 
may, therefore, conceive the heat liberated in respiration to be of 
two sorts: a part of it useful in certain organisms, or even certain 
cells, in maintaining a bodily or cellular temperature which is the 
optimum or so-called ‘‘normal”’; and another part, in excess of this 
first part, which is waste, to be gotten rid of as promptly as any 
other waste. It is a dangerous product, as the organism in fever 
shows. 
We may, then, regard the end products of respiration, the 
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