926 METABOLISM. 



As the metabolism may be kept at its lowest point by absolute rest 

 of body and inactivity of the intestinal tract, it is manifest that work 

 and the ingestion of food have an important bearing on the extent of 

 metabolism. 



Rest and Work. During work a greater quantity of chemical energy 

 is converted into kinetic energy, i.e., the metabolism is increased more or 

 less on account of work. 



As explained in a previous chapter (X), work, according to the gen- 

 erally accepted view, has no material influence on the excretion of nitro- 

 gen. It is nevertheless true that several investigators have observed, 

 in certain cases, an increased elimination of nitrogen; this increase does 

 not seem to be directly related to the work, but to be caused by secondary 

 circumstances. These observations have been explained in other ways. 

 For instance, work may, when it is connected with violent movements 

 of the body, easily cause dyspnoea, and this last, as FRANKEL l has shown, 

 may occasion an increase in the elimination of nitrogen, since diminution 

 of the oxygen supply increases the protein metabolism. In other series 

 of experiments the quantity of carbohydrates and fats in the food was 

 not sufficient; the supply of fat in the body was decreased thereby, and 

 the destruction of proteins was correspondingly increased. Other condi- 

 tions, such as the external temperature and the weather, 2 thirst, and 

 drinking of water, can also influence the excretion of nitrogen. The 

 prevailing sentiment is that muscular activity has hardly any influence 

 on the metabolism of proteins. 



On the contrary, work has a very considerable influence on the elimi- 

 nation of carbon dioxide and the consumption of oxygen. This action, 

 which was first observed by LAVOISIER, has later been confirmed by 

 many investigators. PETTENKOFER and VOIT 3 have made investigations 

 tions on a full-grown man as to the metabolism of the nitrogenous as well 

 as of the non-nitrogenous bodies during rest and work, partly while 

 fasting and partly on a mixed diet. The experiments were made on a 

 full-grown man weighing 70 kilos. The results are contained in the 

 following table : 



Consumption of 



1 Virchow's Arch., 67 and 71. In regard to disputed views see C. Voit, Zeitschr. 

 f. Biol., 49, and Frankel, ibid., SO. 



8 See Zuntz and Schumburg, Arch. f. (Anat. u.) Physiol., 1895. 

 Zeitschr. f . Biologic, 2. 



