CH. XXVII.] 



THE RESPIRATORY QUOTIENT 



393 



and other carbohydrates) is taken, and greatest when much fat and 

 protein are eaten. The quotient n 2 7 K . is called the respiratory 



absorbed 



4-5 



quotient. Normally it is ^ = 0'9, but it varies considerably with diet, 



o 



as just stated. 



The amount of respiratory interchange of gases is estimated by 

 enclosing an animal in an air-tight chamber, except that there is a 

 tube entering and another leaving it ; by one tube oxygen or air can 

 enter, and is measured by a gas-meter as it passes in. The air is 

 drawn through the chamber, and leaves it by the other tube ; this air 

 lias been altered by the respiration of the animal, and in it the car- 

 bonic acid and water are estimated ; it is drawn into bottles containing 

 a known amount of an alkali ; this combines with the carbonic acid 

 and is increased in weight : the increase in weight gives the amount 

 of carbonic acid; the alkali used in Eegnault and Eeiset's apparatus 

 was potash; Pettenkofer used baryta water; Haldano recommends 

 soda-lime. The water is estimated in bottles containing pumice 

 moistened with sulphuric acid. 



The accompanying drawing (fig. 305) shows the essential part of 



Fio. 305. Haldane's apparatus for estimating the carbonic acid and aqueous vapour given off by an 



animal. 



the simple but effective apparatus used by Haldane. The animal is 

 placed in the vessel A ; air is sucked through the apparatus (which 

 must be perfectly air-tight) by a water-pump at a suitable rate. The 

 arrows indicate the direction in which the air passes. It goes first 

 through two Woulffs bottles, 1 and 2. No. 1 contains soda-lime, 

 which frees the air from carbonic acid ; No. 2 contains pumice-stone 

 moistened with sulphuric acid, which frees the air from aqueous 

 vapour. The pure, dry air next reaches the animal chamber, and the 

 animal gives off to it carbonic acid and aqueous vapour. It passes 

 then through the three bottles, 3, 4, and 5. No. 3 contains pumice and 

 sulphuric acid, which removes the water ; No. 4 contains soda-lime, 

 which absorbs the carbonic acid ; and No. 5 contains pumice and sul- 

 phuric acid, which absorbs any water carried over from bottle 4. The 

 'increase of weight in bottle 3 at the end of a given time (e.g. an hour) 

 is the weight of water given off by the animal in that time ; the in- 



