312 



THE HUMAN MOTOR 



Fw.220. 

 Tissot's automatic spirometer. 



amount by which the indication is defective. According to 

 whether a is positive or negative, it is added or subtracted from 

 the volume indicated (fig. 219). 



Tissot's automatic spirometer (fig. 220) can be relied upon for 

 correct measurements. It consists of a very thin (-fa of a milli- 

 metre) copper bell C. fitted on its internal wall with two very light 



