METABOLISM, NUTRITION AND DIETETICS 529 



The nitrogen is contained chiefly in the muscles, glands, and 

 nervous system, and in the constituents of the connective tissues, 

 which yield gelatin, various mucoids, and elastin. The ordinary 

 proteins make up about 9 per cent, of the weight of the body, or 

 22 per cent, of its solids; the albuminoids or sclero-proteins (gelatin- 

 yielding material, etc.) (p. 2) about 6 per cent, of the body- weight. 

 Nitrogen exists in proteins to the extent of 16 per cent., so that the 

 6-5 kilos of protein of a yo-kilo body contain about i kilo of nitrogen. 



The carbon is contained chiefly in the fat, which forms a^very 

 large proportion of the water-free substance of the body, and in the 

 proteins. A small amount is present as calcium carbonate in the 

 bones. In the body of a strong young man weighing 68-6 kilos, 

 Voit found the following quantities of dry fat in the various 

 tissues : 



Adipose tissue - - 8809-4 grammes. 



Skeleton - 2617-2 ,, 



Muscles - 636-8 



Brain and spinal cord - - 226-9 

 Other organs 73-2 ,, 



Total - 12363-5 



equivalent to 18 per cent, of the whole body- weight, or 44 per cent, 

 of the solids. In dry fat rather more than 75 per cent, of carbon 

 is present, and in protein about 50 to 55 per cent. ; so that while 

 the fat of the body analyzed by Voit contained more than 9 kilos 

 of carbon, only about a third of this amount would be found in the 

 proteins. 



In the fat there is, roughly speaking, 12 per cent, of hydrogen, 

 in proteins only 7 per cent. ; so that from three to four times as 

 much hydrogen is contained in the fat of the body as in its proteins. 



Oxygen forms about 12 per cent, of fat, and 20 to 24 per cent, of 

 proteins ; the protein constituents of the body, therefore, contain 

 about as much of its oxygen as the fat. 



Of the inorganic salts calcium phosphate, Ca 3 (PO 4 ) 2 , is much the 

 most abundant owing to the large amount of it in bone, in the ash 

 of which it is found to the extent of 83 per cent., along with 13 per 

 cent, of calcium carbonate. 



Nitrogenous Equilibrium. It is a matter of common ex- 

 perience that the weight of the body of an adult may remain 

 approximately constant for many months or years, even when 

 the diet varies greatly in nature and amount. And not only 

 may the weight remain constant, but the relative proportions 

 of the various tissues of the body, so far as can be judged, may 

 remain constant too. Here it is evident that the expenditure 

 of the body must precisely balance its income : it must lose as 

 much nitrogen as it takes in, otherwise it would put on flesh ; 

 it must lose as much carbon as it takes in, otherwise it would 

 put on fat. Or, again, the body may be losing or gaining 

 fat, giving off more or less carbon than it receives, while 

 its ' flesh ' (its protein constituents) remains constant in 

 amount, the expenditure of nitrogen being exactly equal to the 



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