FUNCTIONS OF ANIMALS. 



to my lungs by an ordinary inspiration. The mean of a great 

 many trials, made with as much care as possible, gave sixteen^cu- 

 bic inches. I caused a tall and stout man with an expanded chest 

 to accustom himself to breathe through a tube without any ef- 

 fort. The quantity which he expelled at a single expiration was 

 also sixteen cubic inches. From these trials, corroborated as 

 they are by the experiments of Allen and Pepys, I am dispos- 

 ed to conclude that the quantity of air drawn into the lungs at 

 each inspiration is sixteen cubic inches, or about T ^th of the whole 

 air that the lungs are capable of containing. Now, as the num- 

 ber of inspirations in 24 hours is 28,800, it is clear that the vo- 

 lume of air taken into the lungs in 24 hours averages 240,800 

 cubic inches, or 266f cubic feet, or 10 avoirdupois Ibs. weight 

 of air. 



2. There is a great diversity in the opinion of different expe- 

 rimenters respecting the ratio which subsists between the volume 

 of air inspired, and that which is expired. According to Davy, 

 air, by a single inspiration and expiration, is diminished from ^th 

 to jfio th part of its bulk.* In the numerous and accurate expe- 

 riments made by Allen and Pepys on a very large scale, the 

 average diminution was little more than half a per cent, and 

 even this seems to have been owing rather to unavoidable inac- 

 curacy than to real absorption. In the experiments of Berthol- 

 let, conducted also with very great care, the diminution varied from 

 0*69 to 3*70 per cent.f I made many years ago numerous ex- 

 periments by enclosing animals in a large glass receiver, through 

 which a gentle current of atmospherical air was constantly pass- 

 ing. On making the requisite allowance for the absorption of a 

 little carbonic acid gas by the water in the vessels through which 

 the air passed, I found that there was no diminution whatever in 

 the volume of air by passing it through the lungs. But the case 

 was very different when an animal was confined in a bell glass, 

 and obliged to breathe the same air for a long time. The volume 

 was always diminished, and the diminution always increased as 

 the quantity of air which the animal breathed was diminished. 

 In one case a rabbit was made to breathe a very small quantity 

 of air. The animal died almost immediately ; but the volume of 

 the air was reduced to one-third of its original bulk. From 

 these experiments it may, I think, be concluded that in ordinary 



* Davy's Researches, p. 431. f Mem. d'Arcueil, ii. 461. 



