342 



ESSENTIALS OF PHYSIOLOGY. 



and shown in fig. 129, may be employed. The animal, e.g. a mouse or 

 guinea-pig, is placed in a vessel through which is drawn a current of 

 air, freed from carbonic acid and water by passing it through soda lime 

 and sulphuric acid. The water in the air leaving the chamber is ab- 

 sorbed by pumice saturated with sulphuric acid, in the tubes B B ; these 

 are weighed before and after the experiment, the increase in weight re- 

 presenting the water given off by the animal. The carbonic acid 

 evolved is absorbed in the tube, which contains soda lime, and the water 

 taken up from the soda^lime is absorbed by sulphuric acid ; these two 

 tubes are weighed before and after the experiment. The amount of 

 oxygen taken up by the animal is determined indirectly by subtracting 



A B C B B A B M 



FIG. 129. Haldane-Pembrey respiration apparatus for mouse. 



(From Practical Physiology, by Pembrey and others.) 

 A, soda lime ; B, H 2 S04 ; C, chamber for animal ; M, gas meter. 



the loss in weight of the animal during the experiment from the total 

 weight of carbonic acid and water given off. 



The respiratory exchange serves as an index of the total oxidative 

 processes taking place in the body, just as the amount of oxygen used, 

 and carbonic acid evolved, by a single organ indicate the functional 

 activities of that organ. It is not influenced by the nature of the 

 food which is consumed, but is very greatly modified by the functional 

 activity of the animal. During exercise the chemical changes taking 

 place in muscle are increased, heat is evolved, and more oxygen is used 

 in the body ; since the muscles form about 40 per cent, of the total 

 weight of the body, the respiratory exchange during exercise may be 

 eight to ten times greater than during rest. . 



RESPIRATORY EXCHANGE IN MAN. (BENEDICT AND CATHCART.) 



