EXCHANGE OF MATEEIAL 11 



Oppenhei merlon rabbits and dogs negative this supposition. In 

 any case it may be considered without appreciable inaccuracy 

 that in researches upon metabolism the total quantity of nitrogen 

 contained in the urine, sweat, and faeces represents the whole 

 amount of nitrogen derived from the protein consumed. 



The nitrogen discharged in the urine in twenty-four hours by an 

 adult man amounts on an average to 15-16 grms., but is subject to 

 considerable variations according to the quantity of nitrogenous 

 food and the different conditions peculiar to the person in question. 

 During the secretion of sweat there is discharged from the 

 skin in addition to water a certain quantity of solid nitrogenous 

 substances, especially in the form of urea. In the profuse sweating 

 caused by a Turkish bath, and also by heavy muscular work, the 

 quantity of nitrogen lost by the skin may, according to 

 Argutinsky's researches, amount to as much as 0'25-0'26 grrn. 

 According to Atwater and Benedict the quantity lost through the 

 skin by a man at rest and exposed to the ordinary temperature of 

 a room is 0'025 grm. per day, whereas the corresponding figure for 

 a man at work is 0'29. In researches on metabolism it is, however, 

 usual without incurring any serious error to leave out of account 

 the nitrogen lost through the skin. In the same way we may 

 leave out of our reckoning the quantity of nitrogen lost with the 

 desquamation of the horny substance of the epidermis, and the 

 falling out of hair, a loss which was exaggerated by Moleschott 

 owing to faulty methods. 



The nitrogenous substances contained in the faeces may arise in 

 two ways : some represent the remains of incompletely digested food 

 which have not been absorbed, and others are excretory products 

 eliminated with various digestive juices, and mixed with degenerate 

 epithelial cells and intestinal bacteria. The non-utilised remains 

 of food disappear from the faeces during fasting and when the 

 food is devoid, or almost devoid, of protein. According to 

 the researches of Kubner, Rieder, Tigerstedt, and Eenvall the 

 faeces formed daily in the intestines of a fasting man contain on 

 an average 01 1-0 "35 grm. of nitrogen ; when the diet is either 

 poor in nitrogenous substances or totally devoid of them, they 

 contain 0'5-l-5 grms. of nitrogen. We may therefore conclude 

 that the quantity of nitrogen discharged with the faeces as 

 a metabolic product is by no means negligible. It may be 

 estimated as an average of 1 grm. per day, inclusive of that 

 contained in the bacteria. It is, however, certain that with an 

 ordinary mixed diet, a considerable portion of the nitrogen 

 discharged with the faeces represents the residue of the food. It is 

 therefore on theoretical grounds equally wrong to add this nitrogen 

 to that found in the urine, thus reckoning it with the output, 

 or to subtract it from that contained in the food when considering 

 the intake. In both cases, however, the inaccuracy is a negligible 



