THE ADVANTAGES OF A MIXED DIET. 125 



It is impossible to state accurately beforehand just what 

 amount of food any individual will require, but a general 

 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 9J ounces (274 grams) of carbon to replace his 

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

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

 daily loses more water than we take in our food; 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 main- 

 tained on them if the necessary salts, water, and oxygen be 

 also supplied; but such a diet would not be economical. 

 Ordinary proteids contain in 100 parts about 52 of carbon 

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

 get about 3^ 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 to get enough carbon from 

 proteids far more than the necessary amount of nitro- 

 gen must be taken. Of dry proteids 1 pound 2J 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 

 element from the body. Fed on a purely proteid diet a 

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



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 entirely on albuminous substances not de- 

 sirable ? 



