METHODS OF MEASURING RESPIRATORY EXCHANGE 33 



duced is absorbed. The amount of CO 2 is determined usually by 

 titration of an aliquot part with very weak hydrochloric acid. 



FIG. 8. Krogh's apparatus for measuring CO 2 output of very small animals. 

 From " Zeit. f. Allgem. Physiol." 



For somewhat larger animals, and especially for small mammals up 

 to the size of a rabbit, the Haldane apparatus (fig. 9) [1892], which al- 

 lows the determination both of carbon dioxide and oxygen, is extremely 



FIG. g. Haldane's respiration apparatus. From "Journal of Physiology " (Cambridge 



University Press). 



convenient and accurate. The air is deprived of carbon dioxide and 

 moisture by means of soda lime (i) and pumice stone soaked in sul- 

 phuric acid (2). The dry and CO 2 free air is taken through the animal 

 chamber (Ch), which is so arranged that it can readily be weighed with 

 the animal enclosed. From the animal chamber the air passes again 

 through a water absorber (3), a carbon dioxide absorber with soda lime 



3 



