20 ON THE INFLUENCE 



vapour expired need not be taken into the 

 account. 



For the purpose of examining the changes pro- 

 duced on the air, by animals breathing under the 

 different circumstances above mentioned, I con- 

 trived an apparatus, which, although simple in 

 its structure, thas been found very well to answer 

 the intended purpose. It is represented in the 

 accompanying plate, by referring to which the 

 construction and application of it will be easily 

 understood. 



Description of the Apparatus. 



A is a wooden stand, in which is a circular 

 groove, three-fourths of an inch in depth, and 

 the same in width. 



B is a bell-glass, the rim of which is received 

 in the circular groove of the wooden stand. In 

 the upper part of the bell-glass is an opening, 

 admitting a tube connected with the bladder C. 



D is a bottle of elastic gum, having a brass 

 stop-cock, E, connected with it. 



F is a silver tube, of which one end is adapted 

 to receive the tube of the stop-cock, E, while the 

 other extremity, making a right angle with the 

 rest of the tube, passes through a hole in the 

 wooden stand, and projects into the cavity of the 

 bell-glass, where it makes a second turn, also at 

 a right angle, and becomes of a smaller diameter. 

 In the upright part of the tube is an opening G. 



The tubes are made perfectly air-tight, where 



