10 



PHYSIOLOGY 



CHAP. 



when the'person experimented on is in a state of rest. Zuntz has, however, 

 lately introduced modifications of the method, which permit its use in 

 experiments on persons who are moving about. As is shown by Fig. 4, the 



apparatus then becomes port- 

 able as a knapsack. The most 

 important of the alterations 

 made by Zuntz in this appar- 

 atus consists in substituting for 

 the heavy water meter a so- 

 called dry meter, in which the 

 volume of gas is measured by 

 flexible leather bellows. 



The quantitative deter- 

 mination of the water and 

 carbon dioxide contained 

 in the air breathed during 

 a certain time will enable 

 us to estimate accurately 

 the quantity of carbon 

 and hydrogen lost through 

 the lungs and skin. The 

 average results obtained 

 from the study of general 

 metabolism show that 

 about nine-tenths of the 

 carbon introduced in the 

 food are eliminated in the 

 form of carbon dioxide, 

 and only one-tenth is com- 

 bined in the organic pro- 

 ducts of the urine. It was also found that about four-fifths of the 

 total quantity of hydrogen in the food are in the form of water, 

 and only one-fifth leaves the body in the urinary products. 



It is doubtful whether all the nitrogen introduced in the food 

 is found in the nitrogenous products of the urine, sweat, and faeces, 

 or whether a not inconsiderable portion is discharged in a gaseous 

 form with the air expired. The results obtained by Regnault 

 and Reiset, Seegen and Nowak prove that the air expired contains 

 a slight excess of nitrogen, on an average 0'004 grin, in rabbits, 

 O'OO 1 / in dogs, per kgrm. and hour. This fact may be 

 explained by the inaccuracy of our methods of research. Leo, 

 indeed, proved that this excess diminishes in proportion to the 

 care taken to avoid such errors. He reduced the excess in the 

 nitrogen expired by rabbits to less than one- tenth of that found 

 by Seegen and Nowak. 



A certain small quantity of nitrogen might be discharged in a 

 gaseous form with the air expired, owing to the decomposition of 

 the nitrogenous substances introduced in the food. The experi- 

 ments made by Krogh on fertilised eggs and mice and by 



FIG. 4. Portable Apparatus of Zuntz. 



