94 



Physiology. 



near the bottom ; heat an iron rod, and apply the end of it to one end 

 of the notch, and slowly draw the rod around to the other end of the 

 notch (the rod may need to be reheated). After cracking off the 

 bottom of the jar, file the edges so they will not cut the rubber. 



Let each pupil make a drawing, showing the position of the parts in 

 inspiration and in expiration. 



The Movements of Respiration. The process of res- 

 piration consists of two acts, inspiration and expiration. 



. . . . Increased Air 

 Space 



Inspiration Expiration 



Fig. 58. Sections of the Body in Inspiration and Expiration. 



Two Active Forces in Inspiration. In inspiration the 

 principal active forces in the body are, first, the dia- 

 phragm ; and, second, the muscles which raise the ribs. 



Work of the Diaphragm in Inspiration. The diaphragm 

 is a muscle, and when its fibers shorten, the diaphragm is 

 pulled down. In moving down it presses on the abdomi- 

 nal organs, and makes the abdomen protrude forward and 

 sideways. This lowering of the diaphragm increases the 



