276 ELEMENTARY PHYSIOLOGY less. 



should die of starvation ; the loss of power in various 

 operations required for its assimilation overbalancing the 

 gain ; or the time occupied in their performance being 

 too great to permit waste to be repaired with sufficient 

 rapidity. The body, under these circumstances, falls into 

 the condition of a merchant who has abundant assets, but 

 who cannot get in his debts in time to meet his creditors. 



These considerations lead us to the physiological justi- 

 fication of the universal practice of mankind in adopting a 

 mixed diet, in which proteins are mixed with fats and 

 carbohydrates. 



Fats may be taken t(j contain about 80 per cent, of 

 carbon, and carbohydrates about 40 per cent. Now it has 

 been seen that there is enough nitrogen to supply the 

 waste of that substance per diem, in a healthy man, in 

 453 grammes (a pound) of fatless meat which also contains 

 67 grammes (1,000 grains) of carbon, leaving a deficit of 

 200 grammes (3,000 grains) of carbon ; 250 grammes (say 

 half a pound) of fat, or 500 gx-ammes (ratlier more than 

 a pound) of sugar, will supply this quantity of carbon. 



Several apparently simi)le articles of food constitute 

 a mixed diet in themselves. Thus butcher's meat com- 

 monly contains from 30 to 50 per cent, of fat. Bread, 

 on the other hand, contains the protein gluten, and the 

 carbohydrates, starch and sugar, with minute quantities 

 of fat. But from the proportion in which these protein 

 and other constituents exist in these substances, they are 

 neither, taken alone, such physiologically economical 

 foods as they are when combined in the pi'opOrtion of 

 about 200 to 75, or two pounds of bread to three-quarters 

 of a pound of meat per diem. 



There is one largely consumed article of food which is 

 not merely composed of all the various food-stufFs requisite 

 to provide a mixed diet, but contains these substances in 

 the relative amounts most suitable for affording an 

 economical diet as regards the proportion of the nitrogen 

 to the carbon. This food is milk. Milk consists chiefly 



