THE EXPIRED AIR. 333 



of the nitrogen, which is either absorbed or given off, are on the 

 whole too small to exert any special influence on this relation. 

 Very numerous experiments have been made on this subject with 

 all the best appliances of science. The individual results yielded 

 by these investigations will engage our attention at a future page, 

 and we would here only observe, that on an average for every 1 

 volume of absorbed oxygen, there is only about 0'8516 of a volume 

 of carbonic acid in the expired air. We shall presently see, on 

 comparing the investigations of modern experimentalists, that this 

 relation appears to be a somewhat variable one, while the experi- 

 ments of Brunner and Valentin, and of von Erlach, give almost 

 exactly this proportion between the gases. According to Valentin, 

 the interchange of these gases (corresponding to the law of their 

 diffusion) stands in an inverse ratio to the square roots of their 

 densities. 



Attempts have frequently been made to compare the volume 

 of the expired with that of the inspired air. On examining both 

 kinds of air when freed from water, we naturally find a diminution 

 of the volume of air, corresponding to the volume of oxygen which 

 has been absorbed and not converted into carbonic acid. (We 

 must, however, here disregard the small quantity of exhaled 

 nitrogen.) The result will certainly be different when both kinds of 

 air are compared together in a moist state ; since the inspired air is 

 usually not saturated with aqueous vapour, while the reverse is the 

 case with the expired air, it necessarily follows that the tension of 

 the aqueous vapour taken up in the lungs must cause an increase 

 in the total volume of the air. 



We need scarcely observe that the elevation of temperature 

 which the air commonly experiences in respiration, (from 36*2^0 

 37'5 , according to Valentin,) must occasion a corresponding 

 augmentation of volume. 



The quantity of water exhaled by an adult man in a state of 

 rest in 24 hours amounts, according to Valentin, to 506, according 

 to Vierordt to 360, and according to Horn to 350 grammes ; as, 

 however, aqueous air was inspired in the experiments of the last- 

 named observers, the actual loss of water is only 321 grammes. 



We have already shown, that the quantity of nitrogen in the 

 air does not remain precisely the same during respiration. Various 

 views were long entertained in reference to the question, whether 

 nitrogen gas was absorbed or exhaled during respiration ; the more 

 modern investigations of Brunner and Valentin, as well as those cf 

 Regnault and Reiset, have now placed it beyond a doubt that 



