274 Biological Chemistry. 



(1) THE GASEOUS SUBSTANCES. 



Various methods have been devised for the measure- 

 ment of the gaseous products of metabolism. One of the 

 earliest employed, and the simplest in principle, is that 

 due to Pettenkofer. The animal is placed in a chamber 

 which is adapted to its size, and a constant current of air 

 is drawn through, the amount passing being measured by 

 a meter. Continuous analyses are made of samples of the 

 air passing in and that passing out. The outgoing air 

 will contain a smaller amount of oxygen and a larger 

 amount of carbon dioxide than the ingoing air, corre- 

 sponding with the amounts of oxygen consumed and carbon 

 dioxide expired by the animal. Other methods in which 

 the same principle is employed are due to Zuntz and 

 Geppert, and can be readily applied to the human subject 

 for clinical investigation. The nostrils of the subject of 

 the experiment are clamped, and he breathes into a mouth- 

 piece in which the inspired and expired airs are separated 

 by passing through valves of aluminium or animal mem- 

 brane, and the outgoing current passes a delicate meter. 

 By a special contrivance an aliquot part of the outgoing 

 air is made to pass to a gas-analysis apparatus in which 

 its composition is determined. This will represent the 

 average composition of the expired air. The composition ! 

 of the inspired air is that of the atmosphere at the time 

 of experiment. In the method of Regnault and Reiset, I 

 the subject of the experiment is kept in a closed chamber ; 

 containing a given volume of air. The carbon dioxide 

 produced by the animal is absorbed by caustic alkali, 

 which is titrated at the beginning and the end of the 

 experiment. The amount of carbon dioxide produced by 

 the animal during the time of the experiment is thereby 

 ascertained. The absorption causes a diminution of the 



