462 BIOLOGY. [BOOK vn. 



sumption of oxygen proportional to the expenditure of force, and 

 finally that, for a given consumption of oxygen, the developed 

 heat and the muscular labour were in inverse proportion to each 

 other. The force expended in heat is not expended in mechanical 

 labour; and inversely. This is exactly what happens in the 

 experiments of pure physics. For example, when an electro- 

 magnetic motor raises a weight represented by 131 kilogram- 

 mitres, it gives, for the same chemical labour in a calorimeter, 

 308 calories less than in all the experiments. 1 In the same way, 

 every muscular effort corresponds to a greater consumption of 

 oxygen, and an appreciable development of sensible heat ; but 

 this quantity of sensible heat is so much less, for the same weight 

 of absorbed oxygen, in proportion as the mechanical labour 

 accomplished has been more considerable. This general proposi- 

 tion is derived from various experiments, amongst which the 

 most important are certainly those of M. Hirn, of Colmar, 2 who 

 has studied, with regard to the production of heat and of power, 

 men ascending upon a revolving wheel, the steps of which moved 

 on under their feet. He noted the quantity of carbonic acid ex- 

 haled by the lungs, first in the state of repose, then during labour. 

 He also measured the quantity of air inspired and respired, 

 and simultaneously the total product in kilogrammetres. 



The experiments of M. Y. Kegnault have shown that, in a 

 dog subjected to a mixed alimentation, out of 100 parts of oxygen 

 absorbed, 7 are employed to form water, by combining with the 

 hydrogen of the organic substances. Now the degrees of heat 

 from the combustion of carbon and hydrogen are known ; we can, 

 then, the quantity of extracted carbonic acid being given, estimate 

 the amount of heat produced, and compare it with the kilogram- 

 metres of exterior labour. We thus find that man can utilise in 

 exterior labour about a fifth of the total heat developed by internal 

 combustions. 



1 Matteucci, Revue Scientifique, 1866, No. 50. 



2 Bulletin de la Societt d'Histoire Naturelle de Colmar, 4 aiinee, 1863. 



