Phenomena and laws of letabolism, 



236. Equilibrium of the Metabolism. 



BY this term is meant that, under normal physiological conditions, 

 just as much material is absorbed and assimilated from the food, as is 

 removed from the body by the excretory organs in the form of effete 

 or end-products, the result of the retrogressive tissue changes. The 

 income must always balance the expenditure; wherever a tissue is 

 used up, it must be replaced by the formation of new tissue. As long 

 as the body continues to grow, the increase of the body corresponds to 

 a certain increase of formation, whereby the metabolism of the 

 growing parts of the body is 2'5 to 6'3 times greater than that of the 

 parts already formed (Crusius). Conversely, during senile decay, there 

 is an excess of expenditure from the body. 



Methods. The normal equilibrium of the metabolism of the body is investi- 

 gated (1) By determining chemically that the sum of all the substances passing 

 into the body is equal to the sum of all the substances given off from it. Thus 

 the C, N, H, 0, salts and water of the food, and the inspired, must be equal to 

 the C, H, N, O, salts and water given off in the excreta (iirine, faeces, air expired, 

 water excreted). (2) The j)hysiological equilibrium is determined empirically by 

 observing that the body retains its normal weight with a given diet; so that by 

 simply weighing a person, a physician is enabled to determine exactly the state of 

 convalescence of his patient. 



The tedious process of making an elementary analysis of the metabolic substances 

 was first undertaken in the Munich School by v. Bischoff, v. Voit, v. Pettenkofer, and 

 others. Their observations showed, that in the circulation of materials the C and 

 N were the most important. The total amount of C taken in the food, if the 

 metabolism be in a condition of physiological equilibrium, must be equalled by the 

 C in the C0 2 given off by the lungs and skin (90 per cent.), together with the 

 relatively small amount of C in the organic excreta of the urine and faeces (10 per 

 cent.). With regard to the N, nearly all the N taken in with the food is excreted 

 within 24 hours in the form of urea. A very small amount of nitrogenous matter 

 is excreted in the faeces, while the other nitrogenous urinary constituents (uric 

 acid, kreatin, &c.) represent about 2 per cent, of N. A trace of the N is given off 

 by the breath (p. 255), and a minute proportion in combination, in the epidermal 

 scales (50 milligrammes daily in the hair and nails) and in the sweat. 



That nearly all the N taken in the food reappears in the urine and 

 fasces, as v. Voit showed for carnivora, and Henneberg, Stohman and 

 Grouven for herbivora, and v. Ranke for man, is contradicted partly by 

 old and partly by new observations (Barral, Boussingault, Bischoff, 

 Regnault and Reiset, Seegen and Nowak), which go to show that the 



