METABOLISM 157 



retaining the water, the other the carbon dioxide. From the 

 increase in weight of the sulphuric acid and potassium hydrate, 

 the amount of water and carbon dioxide given off by the person 

 can be calculated. 



The inhaled oxygen can be found indirectly as follows: The 

 sum total of the income (food -f- oxygen) and the body weight at 

 the beginning of the experiment must be equal to the sum of the 

 outgoings and the body weight at the end of the experiment. 

 Hence 



Oxygen = (final weight -f outgoings) (initial weight -j- food). 



For this calculation the weight of the urine, faeces, and food, 

 and also that of the body at the beginning and at the end of the 

 experiment, must be determined. 



In the respiratory apparatus of Regnault and Reiset, the inhaled 

 oxygen is measured directly. It consists of an air-tight chamber, 

 which is supplied from the outside with pure oxygen only, while 

 the carbon dioxide formed is absorbed by potassium hydrate. 

 This causes a decrease in the volume of gas in the chamber, and 

 hence new quantities of oxygen are forced into the chamber. 

 The volume of oxygen used is thus determined, while the potas 

 .sium hydrate holds all the carbon dioxide. 



While the calculation of the respiratory metabolism in the above- 

 described methods includes the gas-exchange of the skin, by the 

 method of Geppert and Zuntz the gas-exchange of the lungs only 

 is determined. In this, the experimenter does not breathe in a 

 closed chamber, but, the nose being closed, he breathes through 

 a closed mouthpiece which is connected with the so-called 

 Miiller's valves which separate the inspired from the expired air. 



By this method also, the oxygen taken up and the carbon 

 dioxide given off is determined directly, for, in measured quanti- 

 ties of inspired and expired air, the oxygen and carbon dioxide are 

 determined by gas analysis. As the amount of air inhaled and 

 exhaled is measured by a gasometer, the total amount of oxygen 

 taken up and of carbon dioxide given off can be calculated. 



Occasionally it may be of interest to know the changes in 

 the sulphur, phosphorus, and the salts. The sulphur and 

 phosphorus of the income are changed to sulphuric acid 

 and phosphoric acid by oxidation, and, as such, they are 

 estimated. In the same way the sulphur and phosphorus 

 of the faeces may be determined. In the urine the sulphur 

 and phosphorus are already oxidized to sulphuric acid and 

 phosphoric acid. 



