736 THE POPULAR SCIENCE MONTHLY. 



exercise of muscular power immediately involves the destruction of a certain 

 amount of muscular substance, of which the nitrogen excreted is a measure. 

 Indirectly, nitrogenized food is a source of power, as, by its assimilation by the 

 muscular tissue, it repairs the waste and develops the capacity for work ; but 

 food is not directly converted into force in the living body, nor is it a source of 

 muscular power, except that it maintains the muscular system in a proper con- 

 dition for work. In ordinary daily muscular work, which may be continued 

 indefinitely, except as it is restricted by the conditions of nutrition and the 

 limits of age, the loss of muscular substance produced by work is balanced by 

 the assimilation of alimentary matters. A condition of the existence of the 

 muscular tissue, however, is that it cannot be absolutely stationary, and that 

 disassimilation must go on to a certain extent, even if no work be done. This 

 loss must be repaired by food to maintain life. A similar condition of existence 

 applies to every highly-organized part of the body and marks a broad distinction 

 between a living organism and an artificially constructed machine, which latter 

 can exert no motive power of itself, and can develop no force that is not sup- 

 plied artificially by the consumption of fuel or otherwise." 



Prof. Flint, in an appendix, has added a calculation of the non- 

 nitrogenized food taken by Weston during his five days' walk, in order 

 "to answer the possible objections of those who may contend that, in 

 his discussion, lie should have included the heat-producing and force- 

 producing power of non-nitrogenized alimentary substances." This 

 calculation is briefly as follows : 



Force-value of nitrogenized food 2,858.79 foot-tons. 



" " loss of weight of the body 1,764.52 " " 



" " non-nitrogenized food, in excess of that re- 

 quired to produce 17,787 heat-units (the 

 amount of animal heat) produced in five 

 days 597.75 " " 



Total 5,221.06 " " 



Deduct the estimated force used in circulation and respira- 

 tion 1,339.29 " " 



Force remaining for muscular work 3,881.77 " " 



; 'The actual work represented by walking three hundred and seventeen and 

 one-half miles is estimated at 4,321.33 foot-tons. This leaves 439.56 foot-tons 

 of work which cannot be accounted for in any way, according to the estimates 

 of the observers quoted, leaving a deficiency of a little more than ten per cent. 



" These calculations show the fallacy of such estimates, and the impossibility 

 of accounting for work actually performed, even when we include the heat- value 

 and the force-value of non-nitrogenized food." 



The estimates of the force used in circulation and respiration, and 

 of the heat produced by the body, were all calculated for a condition 

 of rest, and they are much less than the estimates that should be 

 made for a period of excessive muscular exercise. 



