8 PHYSIOLOGY 



gasometer G. Before mixing with the air of the chamber it passes through 

 a filtering bottle containing caustic potash and also through a meter, which 

 registers the quantity of oxygen entering the chamber. 



(6) Pettenkofer objected to apparatus constructed on the preceding 

 principle, on the ground that in course of time products of the exhalations 

 of the body, which are'injurious to health, accumulate and are not fixed by 

 potash, as is the carbon dioxide. He therefore in collaboration with Voit 



FIG. 2. Apparatus of Hoppe-Seyler. 



invented an apparatus in which there is continual ventilation ; no direct deter- 

 mination of oxygen was made, but only of carbon dioxide and aqueous vapour. 

 Tigerstedt and Sonde"n greatly increased the space in which the subject 

 of the experiment is confined, by making use of an ordinary room with a 

 capacity of 100*6 cubic metres, and with walls, floor, and ceiling rendered 

 impermeable to air by sheets of zinc. By means of a water-pump the air 

 in the room is continually removed and replaced by fresh air from outside. 

 The volume of air is measured by gas meters, and the quantity of carbon 

 dioxide contained in it is ascertained from time to time by samples taken 

 from the total quantity. 



