652 PHYSIOLOGY 



Protein . . . .94 grm. 



Fat ( 45 



Carbohydrate .... 400 



equivalent to a gross calorie value of 2444. 



VIT AMINES ' 



The statement that a diet composed of the five classes of food-stuffs, proteins, 

 fats, carbohydrates, salts and water, is all that is necessary for the maintenance of 

 life is not strictly true. It is found that if rats, for instance, be fed on milk or bread 

 and milk, they can live and grow in a normal manner. If, however, the proteins, 

 fats and carbohydrates be extracted from the milk, purified, and then mixed in the 

 same proportion as they were in the original milk, the animals, if young, cease to grow, 

 and after some days or weeks die. The ordinary nourishing effect may be restored 

 by adding to the artificial mixture an alcoholic extract of milk, or of yeast cells, or of 

 many other living tissues. It was thought by Stepp, who first called attention to 

 this fact, that certain lipoids must be an essential ingredient of the food. Further 

 light has been thrown on the question by the researches of Hopkins and of Funk. 

 The latter has investigated especially the condition known as beri-beri, which is 

 a state of mal-nutrition brought on by an exclusive diet of polished rice, i.e. a rice 

 which has been deprived of its outer coating. This condition does not occur if to the 

 diet be added the dust rubbed off the rice in the process of polishing. A similar con- 

 dition can be produced in fowls and is rapidly cured by addition to the diet of rice 

 polishings or of an alcoholic extract of these polishings, of yeast cells, or of lime juice. 

 It seems that in addition to the five classes of food-stuffs, minimal quantities of certain 

 other substances are necessary in order that the processes of life may proceed normally. 

 How these substances act we do not know, but we must imagine that they have a drug- 

 like effect on some organs of the body and take the place of or give rise to some of 

 the hormones which are essential for the orderly working of the different organs of the 

 body. Funk has given to these substances the name of ' vitamines.' 



RELATIVE PROPORTIONS OF THE DIFFERENT FOOD- 

 STUFFS IN THE DIET OF MAN 



Since we have exact determinations at our disposal of the total energy 

 output of a man under various conditions, it is easy to assign a total diet 

 to each class which shall satisfy these energy requirements. In such a diet 

 fat and carbohydrate are mutually replaceable in proportion to their calorie 

 value, though it seems that in most individuals for the conservation of perfect 

 health a certain minimum amount both of fats and carbohydrates is necessary. 

 Some observers, however, have described an increased output of carbon 

 dioxide as the result of the mgestion both of carbohydrates and of fats, 

 pointing to a stimulating effect on metabolism of these food-stuffs them- 

 selves. If these results are generally applicable, we cannot regard the total 

 energy output of a man on a given diet as affording a criterion of the amount 

 of food necessary for him per day, since it is possible that with a smaller 

 amount of food the stimulating effect on metabolism might be wanting and 

 tnat the functions of the body might be normally performed with a greater 

 economy of material. The stimulating effect of fats and carbohydrates 

 on metabolism has not, however, been universally observed, whereas in the 

 case of proteins every worker has noted an increased metabolism in propor- 



