BIOLOGY. 291 



" 3. In man, the chief materials used foi* the production of mus- 

 cular power are non-nitrogenous ; but nitrogenous mattei-s can 

 also be employed for the same purpose, and hence the greatly in- 

 creased evolution of nitrogen under the influence of a flesh diet, 

 even with no greater muscular exertion. 



"4. Like every other part of the body, the muscles are con- 

 stantly being renewed ; but this renewal is not perceptibly more 

 rapid during great muscular activity than during comparative 

 quiescence. 



"5. After the supply of sufficient albumenized matters in the 

 food of man to provide for necessary renewal of the tissues, the 

 best materials for the production, both of internal and external 

 work, are non-nitrogenous matters, such as oil, fat, sugar, starch, 

 gum, etc. 



" 6. The non-nitrogenous matters of food, which find their way 

 into the blood, yield up all their potential energy as actual energy ; 

 the nitrogenous matters, on the other hand, leave the body with a 

 portion (one-seventh) of their potential energy unexpended. 



" 7. The transformation of potential energy into muscular power. t>>.~«-^ 



is necessarily accomplished by the production of heat within the . . 



body, even when the muscular power is exerted externally. This 

 is, doubtless, the chief and probably the only source of animal 

 heat." 



Dr. Lyon Playfair, at the 1866 meeting of the British Associa- 

 tion, gave the results of experiments which had been tried with 

 feeding rats and dogs for a considerable time on meat totally free 

 from fat, showing that nitrogenous substances could be made into 

 muscular force. With regard to the amount of nitrogenous 

 matter naturally consumed in food, it appeared that in the fare 

 of soldiers of all countries the amount was 4.2 oz. for each man. 

 The ordinary amount of work that a soldier performed might be 

 estimated as raising 48,000 kilometres to the height of a metre. 

 There had been much more done by the soldier, more especially 

 during the late Prussian war, and the forced marches of Sherman. 

 In the discussion that followed, Dr. Edward Smith contended, 1. 

 That there was no prima facie ground for the division of foods by 

 Liebig into heat-formers and flesh-formers, since the latter con- 

 tain cai'bon and hydrogen like the former, which must be available 

 for the production of heat. 2. That his experiments, as well as 

 those of Voit,had proved conclusively that the emission of nitrogen 

 was no measure of muscular waste, since with the most severe ex- 

 ei'tion the excretion of ured, scarcely at all increased. 3. That the 

 emission of carbonic acid is the true measure of muscular action, 

 since he had jjroved in 1860 that the finger could not be kept in 

 motion without increasing the emission of that product, and the 

 emission increased as the exertion increased. He had in the same 

 year called attention to this as the true measure of muscular action, 

 andwa's the first to do so. 4. That whilst the experiments quoted 

 by Prqf. Frankland, to show that the consumption of carbon 

 and hydrogen was the soui'ce of muscular power — those of Fick 

 and Wislicenus — were inconclusive, there was much reason to 

 believe that the conclusions were not far wrong. They were 



