THE ADVANTAGES OF A MIXED DIET. 125 



. 



It is impossible to state accurately beforehand ju\t what 

 amount of food any individual will require, but a genera 

 idea may be arrived at by taking the average daily losses, by 

 excretion, of a man, as determined by many experiments 

 made on different persons. Such experiments show that a 

 man of average size and doing ordinary work needs rather 

 more than 9^ ounces (274 grams) of carbon to replace his 

 loss of that element; and about T 7 7 of an ounce of nitrogen 

 (20 grams). Some hydrogen is also required, as the body 

 daily loses more water than we drink; and this extra 

 amount implies a loss of hydrogen combined with oxygen 

 in the body to form water. 



The Advantages of a Mixed Diet. Since proteid foods 

 contain carbon, nitrogen, and hydrogen, life may be kept 

 up on them along with the necessary salts, water, and oxy- 

 gen; but such a form of feeding would be anything but eco- 

 nomical. Ordinary proteids contain in 100 parts about 52 

 of carbon and 15 of nitrogen, so a man fed on them alone 

 would get about 3J parts of carbon for every 1 of nitrogen. 

 His daily losses are not in this ratio, but about 13.7 parts 

 of carbon to 1 of nitrogen; and so to get enough carbon 

 from proteids far more than the necessary amount of nitro- 

 gen must be taken. Of dry proteids 1 pound 2| ounces 

 (527 grams) would yield the necessary carbon, but would 

 contain 2| ounces (79 grams) of nitrogen, or four times 

 more than is necessary to cover the daily losses of that ele- 

 ment from the body. Fed on a purely proteid diet a man 

 would, therefore, have to digest a vast quantity to get 

 enough carbon, and in eating and absorbing it, as well as 



What is the average daily loss of carbon from the body? Of 

 nitrogen? Does a man need hydrogen also in his food? Why? 



On what group of foodstuffs can life be maintained without any 

 others? Why is feeding only on albuminous substances not desira- 

 ble? 



