376 



RESPIRATION 



[CH. XXIV. 



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

 proteid are eaten. The quotient -~. 2 ^ , - p is called the respiratory 



4*5 



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



o 



as just stated. It varies also with muscular exercise as the output of 

 carbonic acid is then increased both absolutely and relatively to the 

 amount of oxygen used up. 



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 

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

 bonic acid and water are estimated ; the carbonic acid is estimated by 

 drawing the air through tubes containing a known amount of an 



Fia. 386. Haldane's apparatus for estimating the carbonic acid and aqueous vapour given oft" by an 



animal. 



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 ; Haldane recommends soda-lime. The 

 water is estimated in tubes containing pumice moistened with sul- 

 phuric acid. 



The accompanying drawing (fig. 336) shows the essential part of 

 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 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, 



