of Respiration at different Periods of the Day. 403 



The air respired was in most cases retained in a caoutchouc 

 (" Mackintosh") bag furnished with a brass stop-cock and 

 connecter, and capable of containing 1000 cubic inches. It 

 was invariably filled by successive respirations, and great care 

 was taken to obviate the possibility of inspiring any air that 

 had been once respired. 



The mode of conducting the experiments was as follows : — 



The caoutchouc bag having been filled with respired air, 

 the long graduated tube (with its stop-cocks annexed) having 

 been swilled out with distilled water, and drained, and a small 

 evaporating vessel filled with lime-water, the tube with its 

 stop-cocks was screwed to the connecter of the stop-cock of 

 the caoutchouc bag. The bag was laid upon a chair, while 

 with the knee considerable pressure was exerted upon it, and 

 having opened all the communications between the interior of 

 the bag and the atmospheric air, the pressure upon the bag 

 was continued until about 200 cubic inches of its contents 

 had passed through the tube. The cock at the further ex- 

 tremity of the tube was now closed, and the pressure upon 

 the bag being continued with increased force, the cock at the 

 nearer extremity of the tube was closed. Having secured the 

 stop-cock of the caoutchouc bag, the tube with its own stop- 

 cocks was disconnected. (It is evident that the air included 

 within the tube must be under pressure ; and the object for 

 producing this effect is, that the small quantity of atmospheric 

 air that is retained below the plug of the cock shall be dis- 

 placed when the extremity of the cock is immersed in the 

 lime-water. The accomplishment of this object is fully known 

 by the gurgling noise that accompanies the opening of the 

 cock after its immersion.) 



The stop-cock terminating one of the extremities of the 

 tube was now inserted into the vessel that contained the lime- 

 water : the plug was turned for the free egress of the atmo- 

 spheric air retained below it, and for the subsequent ingress 

 of the reagent ; the lips were applied to the orifice of the 

 upper stop-cock, and the process of exhaustion havin«T been 

 commenced, the upper plug was gently turned, and the ex- 

 haustion steadily continued until the reagent had risen so as 

 to occupy about .SO or 40, or more, of the lower divisions of 

 the tube. The upper stop-cock was then secured, and after 

 a moment's pause the lower one was secured. The number 

 of divisions unoccupied by the lime-water were now noted, 

 the tube being held upright, and the lower surface of the 

 water observed. 



The finger was applied to the lower orifice of the cock 

 which had been immersed, in order to retain that portion of 

 2D2 



