THE ANIMAL AS A PRIME MOVER. 323 



transformations of the vital machine may in some way possibly be 

 illustrated. 



As has elsewhere been suggested, it seems certain that all the inter- 

 nal operations of the body, all the various methods of energy transfor- 

 mation, must result in final reduction of their resultant total to the 

 form of heat energy, and in that form they pass away from the system. 

 This conclusion is confirmed by the experiments of Eubner, who finds 

 that the radiated heat of the animal body precisely measures the cal- 

 orific power of the food utilized by assimulation. 1 



The internal tvorli of the vital machine, as now computed, amounts to 

 43 per cent of the energy supplied less the amount of rejected potential 

 energy of unassimilated food. Neither quantity has as yet been pre- 

 cisely determined. Estimates have been made, however, and possibly 

 sufficiently approximate for present jrarposes. 



Letheby, for example, proposes the following for an average day of 

 the average workingman at his usual vocations involving some manual 

 labor : 



Foot-pounds, external work, actual labor 1, Oil, 670 



Work of the circulation 500,040 



Work of respiration 98, 496 



Total foot-pounds 1, 610, 206 



Adding to this probably very rough estimate the 3,734,400 — 598,536 = 

 3,135,864 for heat not due to these causes, we have a total of 4,746,070 

 foot-pounds, or about one-half of all the energy supplied. Reckoning 

 the work, as before, at 2,000,000 foot-pounds, the total becomes five- 

 eighths the energy supply. 



This leaves at least three-eighths to be accounted for, and if we may 

 take the proportion of blood taken to the brain as a measure of its 

 demand for energy, and, as estimated by Flint, at about 10 per cent, 

 we still have abont 25 per cent as unaccounted for; but it is certain 

 that a part, perhaps a large part, of the heat rejected from the system 

 comes of internal fluid friction and energy transformations, and it is 

 also certain that some of the food escapes digestion and assimilation. 

 In fact, the loss in the latter form of supplied energy has been com- 

 puted in some cases as fully 25 per cent. 



It would thus appear possible, if not extremely probable, that the 

 full amount of the potential energy of the food actually assimilated 

 may be accounted for in one or another form of the resultant energies 

 visible or sensible as external, and as essential internal, work in the 

 vital machine. Just what internal work the external heat flow may 

 represent it is impossible to say positively; but assuming that all the 

 energy expended in the circulation of the fluids of the body, all the 

 work of friction so appears, and that all energy of internal mechanical 

 work of other sorts and of all chemical processes occurring within the 



1 Zeitschrift fur Biologic, XXX, 1893, page 73. 



