460 A MANUAL OF PHYSIOLOGY 



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

 system, and in the constituents of the connective tissues, which yield 

 gelatin, chondrin, and elastin. The proteids make up about 9 per cent, of 

 the weight of the body, or 22 per cent, of its solids ; the albuminoids 

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

 Nitrogen exists in proteids to the extent of 15 per cent., so that the 6*5 kilos 

 of proteid of a yo-kilo body contain nearly i ki'o of nitrogen. 



The carbon is contained chiefly in the fat, which forms a very large pro- 

 portion of the water-free substance of the body, and in the proteids. A 

 small amount is present as calcium caibonate 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 - ... 1 2363' 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 proteid about 50 to 55 per cent. ; so that while the fit 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 proteids. 



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

 teids only 7 percent. ; so that from thiee to four times as much hydrogen 

 is contained in the fat of the body as in its proteids. 



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

 teids ; the proteid 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 

 proteid constituents) remains constant in amount, the ex- 

 penditure of nitrogen being exactly equal to the income. 



