THE ANIMAL AS A PRIME MOVER. 321 



(4) The internal energies, though useful, objective forms, each being 

 utilized in the performance of its special work, are subject to a final 

 transformation, and are at last converted into heat and passed outward, 

 to be excreted by the skin and the lungs. 



The latest researches indicate very positively that the production of 

 heat in the vital prime mover is partly due to nutrition and tissue 

 repair, or rather its breaking down, and not all necessarily derived 

 from the simple and direct oxidation of the combustible matter of food. 

 It is even uncertain whether the potential energy of food considered as 

 a fuel and of its combustion in air is to be taken as precisely measuring 

 its energy available for the work of the vital machine. Chauveau con- 

 siders the glycogenic product of the liver distributed to the tissues the 

 source of all mechanical and thermal energy. The sound animal 

 machine can work vigorously about eight hours a day; the remaining 

 sixteen hours are devoted to repair, reconstruction, and energy storage. 

 Eight hours each day, one-third of life, is given especially to the repara- 

 tion of the brain and mental powers. 



Dr. Edward Smith has shown, by experiment upon himself, that the 

 inspiration of air and the production of carbon dioxide may vary in the 

 proportion of 1 to 10, accordingly as the individual lies sleeping or 

 actively exerts himself in the treadmill or in running at top speed, the 

 exhalations of 0O 2 ranging from 5.5 grains to 45 grains per minute. 1 

 The quantity becomes, for the given case, 6 grains when standing, 

 20 when walking, and 25 or 30 when walking rapidly. The variation 

 seems to be approximately, in Smith's tables, as the square root of 

 the speed of the pedestrian. Since the total work of the machine 

 must vary as the velocity of overcoming a fixed resistance, as the 

 cube of velocity where the resistance increases with the speed square, 

 as is here presumably the fact, it would seem from these facts that 

 the interior resistance must be a rapidly increasing proportion of 

 the total work performed, internally and externally, a deduction which 

 is confirmed by constant and familiar experience. The experiments of 

 the same investigator, however, seem to prove the variation of the 

 exhalations when at rest, directly with the difference between the exter- 

 nal and the internal temperatures ; which, if corroborated fully, would 

 indicate the heat of oxidation in the body to be ordinarily employed 

 principally in the maintenance of its warmth at the standard point. 

 This makes it advisable to ascertain more exactly what energy is meas- 

 ured by the chemical actions resulting in the production of other 

 rejected compounds, solid and liquid, and to learn, if possible, whether 

 chemical action in one case produces the demanded thermal energy 

 and in others the required chemical or other motive energy. 



These various deductions indicate that one-tenth or thereabouts of 

 the energy of oxidation in the tissues of the body and in its capillaries 

 fiually produces work of various kinds; that nine-tenths passes as 



'Foods. International Series. New York : D. Appleton & Co, 

 SM 96 21 



