ENERGY FROM WASTE OF TISSUE. 529 



taken : 2 oz. of flesh-formers in the daily food suffice to keep a 

 man alive; 3J oz. of flesh-formers must be in the daily food 

 to preserve a man in health under moderate exercise ; 6 oz. of 

 flesh-formers ought to be in the daily food when a man is sub- 

 jected to hard labour ; 2-J- oz. of flesh-formers, or the difference 

 between the quantity of flesh-formers required to keep the body 

 in health under moderate exercise, and the quantity of the same 

 necessary for a hard day's work, represent a man's productive 

 labour in a day that is to say, flesh-formers to the amount of 

 2 J oz., over and above the SJ oz. indispensable daily for health 

 and moderate exercise, render a man capable of severe exertion 

 during a working day of 10 hours. So much does this corre- 

 spondence between the supply of proper food and the capability 

 of efficient exertion stand in the relation of antecedent and 

 consequent, that it is said railway contractors set a watch on 

 their men at meal-times, and take an early opportunity of 

 dismissing from their service such men as fail to eat what they 

 consider a sufficiency of food. 



The force, then, which an animal expends in labour is derived 

 solely from the potential energy in the flesh-formers of the 

 food, and the oxygen by which these flesh-formers, or their re- 

 presentatives in the muscular tissue, are chemically transformed. 

 Professor Playfair says, " The daily waste of tissues, secreted as 

 urea by the kidneys, would, after supporting fully all the vital 

 functions of the body and the limited mental functions of a 

 labourer, enable him to execute such mechanical labour as 

 would raise about 1,000,000 Ib. to the height of one foot." 

 But 792,000 Ib. to the height of one foot being the utmost 

 that the hardest-working labourer can accomplish of evident 

 mechanical labour, the difference, or the force necessary to 

 raise 208,000 Ib. to the height of one foot, is that expended on 

 animal heat, and vital and mental work. 



The following is Moleschott's estimate of the admixture of 



2L 



