EQUILIBRIUM OF THE METABOLISM. 355 



We may also include many substances of unknown constitution which act upon the 

 gustatory organs, e.g., dextrin, and substances in the crust of bread and in meat 

 which has been roasted. 



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. During the period of growth, 

 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. Conversely, during senile decay, there is an excess 

 of expenditure from the body. 



Methods. The normal equilibrium of the metabolism of the body is investigated (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, N, H, 0, salts and water given off in the excreta 

 (urine, faeces, air expired, water excreted). (2) The physiological 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 con- 

 valescence 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. 



Circulation of C. In the circulation of materials 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). 



Circulation of N. Nearly all the JV taken in with the food is excreted within 

 twenty-four 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, 

 kreatinin, &c.) represent about 2 per cent, of N". A trace of the N is given off by 

 the breath ( 124), and a minute proportion in combination, in the epidermal scales 

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



Deficit of N. That nearly all the N taken in the food reappears in the urine and 

 faeces, as was stated by v. Voit to be the case in the carnivora and in the herbivora, 

 and by v. Ranke in man, is contradicted partly by old and partly by new observa- 

 tions, which go to show that the whole of the N cannot be recovered from these 

 excretions, but that on the contrary there is a considerable deficit. 



According to Leo, only 0*55 per cent, of the albumin transformed within the body (assuming 

 15 per cent. N in albumin) gives off its N in the form of gaseous N (according to Seegen and 

 Nowak 12 times more). In every exact analysis of the metabolism of N this gaseous excretion 

 of N must be taken into account. 



The excretion of N after food does not take place regularly from hour to hour, but it increases 

 at once and distinctly, reaches its maximum in five to six hours, and then gradually falls. The 

 same is true of the excretion of S and P ; but in these cases the maximum of excretion is reached 

 at the fourth hour. When fat is added to a diet of flesh, the excretion of N and S is uniformly 

 distributed over the individual hours of the day (v. Voit and Feder). 



The nitrogenous constituents in the body during metabolism become poorer in C, and richer 

 in N and O. Thus in albumin to 1 atom of N there are 4 atoms C ; in gelatin, 3 C ; in 

 glycocoll, 2 C; in kreatin, 1 C ; in uric acid, 1 C ; in allantoin, 1 C ; in urea, only"^ atom 

 of C. 



The H leaves the body chiefly in the form of water a part, however, is in 

 combination in other excreta ; the is chiefly excreted as C0 2 and water ; & little 

 is given off in combination in other excreta ; water is given off by evaporation 

 from the lungs and skin, and also in the urine and faeces. As H is oxidised to 

 H 2 0, more water is excreted than is taken in. Most of the readily soluble salts 



