i EXCHANGE OF MATEEIAL 9 



(c) All the various forms of apparatus hitherto described are generally 

 used for experiments lasting several hours or even whole days. If, on the 

 other hand, we desire to study gaseous exchange for a brief period, and more 

 especially if we wish to ascertain the influence of certain conditions of short 

 duration, such as muscular work, we make use of those methods in which the 

 respiratory tract is placed in direct connection with the apparatus. It is 

 obvious that in these methods only the gaseous exchange of the lungs is 

 taken into account, but this is to a certain extent justified by the fact that 

 gaseous exchange is effected mainly through the lungs. According to Zuntz 

 only 1 per cent of the carbon dioxide eliminated and the oxygen absorbed in 

 normal conditions passes through the skin. (See Vol. I. Chap. XXIII.) 



The principle on which the various methods devised for this purpose are 

 based is that of breathing through the mouth, the nasal passages having 



FIG. 3. Apparatus of Zuntz. 



been closed by a clip, by means of a tube fitted with two valves of the kind 

 invented by Miiller, which separate the air inhaled from that exhaled. The 

 valves used by Lov4n and Speck are of this type. 



Speck, who with Smith was the first to make experiments of this kind, 

 used two separate gasometers, from one of which he drew the air inspired, and 

 in the other collected the air expired. 



Geppert and Zuntz simplified and improved the method, by replacing 

 the cumbrous gasometers by a gas meter and confining themselves to 

 samples of the expired air, the composition of the atmospheric air inhaled 

 being already known and constant 



The apparatus of Geppert and Zuntz consists of three parts, as shown in 

 Fig. 3 : a valvular apparatus which separates the air inspired from that 

 expired, allowing only the latter to pass into the meter ; a gas meter, and an 

 apparatus for the analysis of samples taken from the total quantity of the 

 air expired and the volumetric determination of the quantities of both carbon 

 dioxide and oxygen. This apparatus is used for laooratory researches and 



