138 FOODS 



carbohydrates, inorganic salts, and water), five, all except water, are 

 sources of energy by their metabolism, chiefly katabolism, in the body. 

 It is possible that the ingested water also may be in part decomposed, 

 or, more probably, may unite with the simple products of katabolism in 

 anabolic processes, thus producing energy; of this little is definitely 

 known. Of the familiar six, three only are sources of tissue considered 

 as active bioplasm (that is, excluding fat) namely, proteids, inorganic 

 salts, and water. Carbohydrates and fats are sources of tissue-fat, but 

 the latter is- relatively, at least, unimportant in the actual life of the 

 animal in health, and in this relation is not considered as tissue- 

 protoplasm. It is a tissue, but one of a special sort. 



THE GRAND DIVISION OF NUTRIENTS. 



Sources of bioplasm. Sources of energy. 



Proteids. Proteids. 



Inorganic salts. Inorganic salts. 



Water Fats. 



Carbohydrates. 



Albuminoids. 



Water (?). 



Of the three sources of protoplasm, proteids alone are by themselves 

 producers of protoplasm, for, of course, feeding inorganic salts or water, 

 or both together, and nothing else, could do nothing toward continuously 

 supporting life. Actual starvation is, however, excepted, for then water 

 will prolong vitality; in case of the higher animals entire lack of water 

 kills much more quickly than entire lack of other nutrients. (Lack of 

 all sleep destroys life sooner than lack of either food or drink.) 



This division of the proximate principle of foods into two classes, one 

 of which supplies to the animal both active tissue and energy, and the 

 other of which furnishes only energy, is of the largest importance in 

 the physiology of nutrition. Notwithstanding, the division is far from 

 absolute, in that even a carnivorous animal requires for continued 

 existence at least a very small proportion of fats and carbohydrates as 

 well as the proteids, the mineral salts, and water mentioned in the 

 table. The reason for this is, as has already been stated, the com- 

 position of the living substance. As will be recalled, it seems always 

 to contain some fat and especially some carbohydrate. The char- 

 acteristically vital particle probably consists of all of these molecules 

 in some sort of combination or other proteid, carbohydrate, fat, salts, 

 and water in one unstable vital mass. However, in general terms, an 

 animal can live on proteids, inorganic salts, and water, but not on fats, 

 carbohydrates, salts, and water, singly or in any combination. This 

 gives proteid a preeminence as an alimentary component, a preeminence 

 which men in general as well as physiologists appreciate. The immedi- 

 ate reason for this superiority, of course, is obvious: the proteids alone 

 (save as noted below) contain nitrogen, available for the building of 

 new albumin in the ever-wasting animal tissues. In the nitrogen most 



