METABOLIC EQUILIBRIUM. 431 



times as active a metabolism as parts of the body already formed. On 

 the other hand, in the years of senile debility a certain excess of bodily 

 expenditure is to be considered as a normal phenomenon. 



Method. The normal metabolic equilibrium in the organism may be recog- 

 nized: i. By determining chemically that the sum of all the egesta, given off by 

 the body within a certain period of investigation, corresponds to the sum of the 

 ingesta furnished by the food. In this connection the amount of carbon, nitrogen, 

 hydrogen, oxygen, and salts, together with the water of the food and the oxygen 

 of the inspired air, must be equal to the carbon, nitrogen, hydrogen, oxygen, the 

 salts and the water in the excretions (urine, feces, expired air, evaporated water) 

 of the organism. 2. The physiological equilibrium of metabolism may further 

 be recognized in a purely empirical way from the fact that with a suitably selected 

 diet, the body performing its ordinary functions is able to maintain its normal 

 weight. Thus, this simple procedure of weighing makes it possible for the phy- 

 sician to inform himself quickly and with certainty concerning the metabolism 

 of his patient or convalescent. The tedious method of elementary metabolic 

 analysis was first successfully undertaken particularly by the Munich investi- 

 gators, v. Bischoff, v. Voit, v. Pettenkofer and others. It was soon apparent 

 that of all the elements the greatest importance was to be assigned to the passage 

 through the body of carbon and nitrogen. 



The total amount of carbon taken with the food (which is ascertained by 

 elementary analysis of a sample of each article of diet, or is calculated from re- 

 liable analyses of the articles of food) must, in complete metabolic equilibrium, 

 correspond to the carbon in the carbon dioxid contained in the expired air (90 

 per cent.) from the lungs and the skin. To this there should also be added the 

 relatively small amount of carbon in the organic excrementitious matters 

 of the urine and the feces (10 per cent.), which is to be determined by ele- 

 mentary analysis. As all organic food and all the constituents of the body 

 contain carbon, an increased loss of carbon (as compared with the income) in- 

 dicates that organic matter in excess is being decomposed in the body; on 

 the other hand, diminished excretion of carbon necessarily indicates an ad- 

 dition to the substance of the body. For the exact determination of the car- 

 bon dioxid in the expired air the Munich investigators employed v. Petten- 

 kofer's respiratory apparatus. 



With regard to the nitrogen, which should be determined in the ingesta 

 as well as the excreta by the method of Kjeldahl, it was found that almost 

 all the nitrogen of the ingested food is excreted again in the urine within 24 

 hours, principally in the form of urea. The remaining nitrogenous urinary 

 constituents (uric acid, kreatinin, etc.) furnish only about 2 per cent, of the 

 nitrogenous elimination. In addition, the nitrogen-content of the feces is 

 to be taken into account (from 4 to 5 per cent, in dogs). A small amount of 

 nitrogen also escapes from the organism in the expired air; also a portion with 

 the desquamated epidermal structures (about 50 mg. of hair and nails daily) 

 and in the sweat. 



The opinion that practically all the nitrogen ingested with the food is 

 excreted in the urine and the feces was established for carnivora by v. Voit 

 and Gruber; for ruminants by Henneberg, Stohmann and Grouven, and for 

 man by Ranke. Contrary to this view a number of the older as well as more 

 recent investigators have made the assertion that the total amount of nitrogen 

 cannot be recovered from the excretions mentioned, but that an appreciable 

 nitrogen-deficit exists. 



According to Leo about 0.55 per cent, of the albumin decomposed in the 

 body yields its nitrogen (which may be assumed to amount to 15 per cent.) 

 in the gaseous state. In making exact analyses of metabolism this gaseous 

 excretion of nitrogen must naturally be taken into account. 



In the food nitrogen occurs almost exclusively as a constituent of albu- 

 minous substances. In the excretions it indicates decomposition of 'the 

 albuminous constituents of the body. As proteids contain on the average 

 1 6 per cent, of nitrogen the amount of albumin corresponding to the amount 

 of nitrogen excreted is determined by multiplying the latter figure by 6.25. 

 Nitrogenous equilibrium thus indicates that the albuminous substances in 

 the body are unchanged. If nitrogen is retained gain in weight takes place, 

 principally in the form of muscle ; if there is an excess of nitrogenous excre- 

 tion, consumption of the albuminous constituents of the body must ensue. 



