2 4 o RESPIRATION 



in disease, but each experiment can only be carried on at most for 

 fifteen to twenty minutes. 



(2) A small apparatus, much on the same principle, was used for 

 rabbits by Pfliiger and his pupils. A cannula in the trachea was con- 

 nected with a balanced and self-adjusting spiro meter containing oxygen, 

 and the inspired and expired air separated by potassium hydroxide 

 valves, which absorbed the carbon dioxide. The amount of oxygen 

 used could be read off on the spirometer, and the amount of carbon 

 dioxide produced estimated in the liquid of the valves. 



(3) Elaborate arrangements, such as Pettenkofer's great respiration 

 apparatus, and the still larger and more efficient modifications of it 

 constructed since his time, in which a man, or even several men, can 

 remain for an indefinite period, working, eating, and sleeping: Air is 

 drawn out of the chamber by an engine, its volume being measured 

 by a gas-meter. But as it would be far too troublesome to analyze 

 the whole of the air, a sample stream of it is constantly drawn off, which 

 also passes through a gas-meter, through drying-tubes containing 

 sulphuric acid, and through tubes filled with baryta water. The baryta 

 solution is titrated to determine the quantity of carbon dioxide; the 

 increase in weight of the drying tubes gives the quantity of aqueous 

 vapour. A similar sample stream of the air before it passes into the 

 chamber is treated exactly in the same way, and from the data thus got 

 the quantity of carbon dioxide and aqueous vapour given off can readily 

 be ascertained. The oxygen can be calculated, as the difference be- 

 tween the final body-weight and the original body-weight plus the 

 weight of the carbon dioxide and water eliminated, but may also be 

 directly estimated by special methods. 



(4) Haldane and Pembrey have elaborated a gravimetric method, 

 which is very suitable for small animals. It depends upon the absorp- 

 tion of carbon dioxide by soda lime. (See Practical Ex'ercises, p. 30%) 

 In Atwater's so-called respiration calorimeter, which will be referred to 

 again under ' Animal Heat,' and by which, not only the gaseous metab- 

 olism, but the heat production can be measured in man, the carbon 

 dioxide is estimated in the same way. 



Inspired and Expired Air. The expired air is at or near the body 

 temperature, and is saturated with watery vapour. In ordinary 

 breathing it contains about 4 per cent, of carbon dioxide, while the 

 inspired air only contains a trace. The expired air contains 16 or 

 17 per cent, of oxygen, the inspired air about 21 per cent. There are 

 in addition in expired air small quantities of hydrogen and marsh- 

 gas derived from the alimentary canal, either directly from eructa- 

 tion or after absorption into the blood. Sometimes a trace of 

 ammonia can be detected in the air of expiration, but this is due to 

 decomposition of proteins taking place in the mouth, especially in 

 carious teeth, or in the air-passages and lungs in disease of these 

 organs. It has indeed been shown that the lungs are practically 

 impermeable for ammonia. Expired air is entirely free from float- 

 ing matter (dust), which is always present in the inspired air. The 

 volume of the expired air, owing to its higher temperature and ex- 

 cess of watery vapour, is somewhat greater than that of the inspired 

 air, but if it be measured at the temperature and degree of satura- 

 tion of the latter, the volume is somewhat less. Since the oxygen 

 of a given quantity of carbon dioxide would have exactly the same 



