INCOME AND EXPENDITURE OF THE BODY. 311 



tion of the whole heat liberated in the furnace which can be 

 used to do work. Now in a muscle there is no condenser; its 

 temperature is uniform throughout. So when it contracts 

 and lifts a weight, the energy employed must be liberated in 

 some other form than heat some form which the muscular 

 fibre can use without a condenser. 



Summary. The living Body is continually losing mat- 

 ter and expending energy. So long as we regard it as work- 

 ing by virtue of some vital force, the power of generating 

 which it has inherited, the waste is difficult to account for, 

 since it is far more than we can imagine as due merely to 

 wear and tear of the working parts. When, however, we con- 

 sider the nature of the income of the Body, and of its ex- 

 penditure, from a chemico-physical point of view, we get the 

 clue to the puzzle. The Body does not waste because it 

 works, but works because it wastes. The working power is 

 obtained by chemical changes occurring in it, associated with 

 the liberation of energy which the living cells utilize; and 

 the products of these chemical changes, being no longer 

 available as sources of energy, are passed out. The chemical 

 changes concerned are mainly the breaking down of complex 

 and unstable chemical compounds into simpler and more 

 stable ones, with concomitant oxidation. Accordingly the 

 material losses of the Body are highly or completely oxidized, 

 tolerably simple, chemical compounds; and its material in- 

 come is mainly nncombined oxygen and oxidizable substances, 

 the former obtained through the lungs, the latter through 

 the alimentary canal. In energy, its income is the potential 

 energy of uncombined or feebly combined elements, which 

 are capable of combining or of forming more stable com- 

 pounds; and its final expenditure is kinetic energy almost 

 entirely in the form of mechanical work and heat. Given 

 oxygen, all oxidizable bodies will not serve to keep the Body 

 alive and working, but only those which (1) are capable of 

 absorption from the alimentary canal and (2) those which 

 are oxidizable at the temperature of the Body under the influ- 

 ence of protoplasm. Just as carbon and oxygen will not 

 unite in the furnace of an engine unless the fire be lighted by 

 the application of a match but, when once started, the heat 

 evolved at one point will serve to bring about the conditions 

 of combination through the rest of the mass, so the oxida- 

 tions of the Body only occur under special conditions; and 



