THE TOTAL EXCHANGES OF THE BODY 689 



involves the use of some form of respiration apparatus. The fol- 

 lowing are the chief methods which have been employed for this 

 purpose : 



I. THE METHOD OF HALDANE. This method is extremely 

 convenient when dealing with the gaseous exchanges of small 

 animals, such as mice, rats, guinea-pigs, or rabbits. The animal 

 is placed in the chamber c, which may be simply a wide-mouthed 

 bottle (Fig. 314). This chamber is supplied with a thermometer, 

 and can be kept at any desired temperature by immersion either 

 in warm or cold water. On the inlet side of the bottle is a 

 series of tubes or bottles, some of which contain sulphuric acid 

 and pumice-stone, while the others contain soda lime. On the 

 outlet side of the vessel is a corresponding series of vessels for the 



Soda Lime H,SO 



FIG. 314. Haldane-Pembrey respiration apparatus, 

 c, chamber for animal ; M, gas meter. 



absorption of water and of carbon dioxide. On the further side 

 of these vessels is a gas meter. During an experiment air is sucked 

 through the whole apparatus by means of an aspirator or a water 

 pump, the amount of air passing through the apparatus being measured 

 by the meter. The animal is thus supplied with pure air freed from 

 water vapour and from carbon dioxide. Any water or carbon dioxide 

 produced by the animal is absorbed by the vessels interposed in the 

 course of the outgoing air. These vessels are weighed at the beginning 

 of the experiment and at the end, and the difference in weights will 

 therefore give the amounts of carbon dioxide and water which have 

 been discharged by the animal. 



The intake of oxygen by the animal is determined indirectly. 

 Since it gives off only carbon dioxide and water, and absorbs only 

 oxygen during its stay in the chamber, the loss of weight of the 

 animal during its stay in the chamber, subtracted from the total 

 amount of carbon dioxide plus water it gives off, will represent the 

 amount of oxygen absorbed. 



The advantage of this apparatus is that it can be fitted up in 

 any laboratory, and is accurate for the purposes to which it is applied. 

 It is not, however, appropriate for long-continued experiments or 

 for experiments on larger animals or on man himself. Most of the 



44 



