SEX, REST AND WORK. 867 



lated upon the square meter of surface of body it is lower than in an indi- 

 vidual of medium age. 



The question as to what extent sex specially influences metabolism 

 remains to be investigated. TIGERSTEDT and SONDEN found that in the 

 young the carbon-dioxide elimination, per kilo of body weight as well as 

 per square meter of body surface, was considerably greater in males 

 than in females of the same age and the same weight of body. This 

 difference between the two sexes seems to disappear gradually, and at 

 old age it is entirely absent. The investigations of MAGNUS-LEVY and 

 FALK oppose these observations. They investigated by means of the 

 ZUNTZ-GEPPERT method, not only children, but also adults and old 

 persons of both sexes, but could not observe any positive influence of 

 the sex upon metabolism. 1 



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 (XI), 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 2 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, 3 thirst, and 

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



1 Tigerstedt and Sond6n, Skand. Arch. f. Physiol., 6; Magnus-Levy and Talk, 

 Arch. f. (Anat. u.) Physiol., 1899, Suppl. In regard to metabolism and its relation 

 to the phases of sexual life and especially under the influence of menstruation and 

 pregnancy, see the investigations of A. Ver Eecke (Bull. acad. roy. de med. de Belgique, 

 1897 and 1901, and Maly's Jahresber., 30 and 31). See also Magnus-Levy in v. Noor- 

 den's Handb. d. Pathol. d. Stoffwechsels. 



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

 f. Biol., 49 and Frankel, ibid., 50. 



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



