i EXCHANGE OF MATEEIAL 7 



the place of N as soon as the latter is empty) by the water coming from the 

 cistern in which it is always kept at a constant leveL Before entering the 

 bell-jar the oxygen passes through the filtering bottle M. The fourth tube 

 in the opening of the bell -jar cormnunicates on the one hand with a mercurial 

 manometer a b c, showing the gaseous pressure prevailing in the interior of 

 the system, and on the other hand with a U-shaped tube containing mercury 

 (r" d), which serves for the removal of samples of air from the bell -jar. 



If we determine the composition of the air in the bell-jar before and 

 after the experiment, the quantities of carbon dioxide discharged and 

 oxygen absorbed during the experiment, it is obvious that we can by this 

 method readily ascertain the gaseous respiratory exchange of a small animal 

 during the period of several hours spent by it in the apparatus. 



One of the drawbacks of this method is that the animal is forced to 



FIG. 1. Apparatus of Regnault arid Reiset. 



breathe in a fixed volume of gas, so that during inspiration the gas is 

 rarefied, whilst it is compressed during expiration. This makes the 

 respiratory movements difficult, and is perhaps not without influence on the 

 course of the normal processes of gaseous exchange. Another drawback in 

 the apparatus of Regnault and Reiset is that the absorption of carbon dioxide 

 is both slow and difficult. 



Later methods, based on the same principle as the apparatus of Regnault 

 and Reiset, have endeavoured to obviate this defect. Amongst these methods 

 we may mention that of Grandis (1909) for animals and that of Hoppe- 

 Seyler for man ; the latter we will now describe. 



As will be seen from Fig. 2, the subject of the experiment is shut up in 

 the large chamber A, having a capacity of 4*8 cubic metres, and from which, 

 through two wide tubes, air is alternately withdrawn and restored by 

 means of the pump below, which is kept constantly in motion by a water 

 motor. The air is thus brought into contact with a strong solution of caustic 

 potash, contained in two flasks (#, ), and is thus deprived of carbon dioxide. 

 Oxygen is forced through a narrow copper tube into the chamber by a 



VOL. V B 2 



