152 THE BODY AT WORK 



diet would, of course, be much more varied than this, but it is 

 simpler to express it in these terms. 



Such a diet would hardly answer the requirements of a man 

 doing hard muscular work. Experience shows that he would 

 expect to receive a more liberal supply of energy, and that to 

 obtain it he would increase slightly his allowance of proteins, and 

 very considerably increase the quantity of carbohydrates that 

 he consumed. The diet of European workmen is remarkably 

 constant in the relative amounts of its several constituents, no 

 matter what their nationality or the exact form of their work 

 may be : Proteins, about 135 grammes ; fats, 80 grammes ; 

 carbohydrates, 500 to 700 grammes giving a supply of energy 

 equal to 3,500 to 4,000 kilo-calories. 



Speaking generally, carbohydrates are the source of muscular 

 force, and fats of heat. In warm climates men work on carbo- 

 hydrates. The 'rickshaw men of Japan are said to eat only 

 rice on working days, and to reserve fish for days of leisure. 

 The Japanese, as is well known, consume extremely little fat. 

 The Esquimaux and other inhabitants of high latitudes eat 

 immense quantities of fat. Proteins constitute the luxurious 

 element of a diet. Not only are they more attractive to most 

 palates, and therefore preferred by persons whose dietary is 

 not severely regulated by price, but the body prefers them. 

 It works with greater alacrity when supplied with more protein 

 than, in a strictly physiological sense, it needs. 



The supply of food must exceed the apparent demand. The 

 most efficient of motors cannot convert more than 15 per cent, of 

 the energy potential in its fuel into work. If a man endeavours 

 to obtain a better result than this from his muscular system, 

 if he tries to make his machine do more than 15 units of work 

 for every 100 units of energy with which he supplies it, he does 

 it at the expense of his own tissues. First he loses in weight, 

 owing to the consumption of fat ; then the excess of nitrogen 

 discharged over nitrogen consumed shows that he is burning 

 up the proteins of his own tissues. It is needless to add that 

 the weakness which results puts a stop to excessive work. 

 Muscles, as we shall find when we consider the relation of their 

 output of work to the energy supplied to them, can produce 

 a much better result than the best of engines ; but we are 

 speaking of the body as a whole, which wastes energy in the 



