208 STUDIES IN ADVANCED PHYSIOLOGY. 



organ. When we remember that on an average about every 

 one person in seven is afflicted with this disease, that it car- 

 ries off as its prey more people than pretty nearly all of the 

 more violent contagious diseases combined, and when we 

 remember that by improper ventilation, the crowding of 

 persons into close rooms, this disease is highly communica- 

 ble, we are more than justified in every reasonable effort to 

 prevent its spread, and especially its spread to children, 

 who, on account of their age, may yet happily be free from 

 its fatal touch. 



* 



THE MECHANICS OF RESPIRATION. 



1. Movements of Respiration. In order for the blood 

 to be continually supplied with fresh oxygen it is necessary 

 that this gas should be constantly renewed in the lungs. 

 This renewal is brought about by the movements of respira- 

 tion. The essential feature of all the movements of in- 

 spiration is an enlargement of the chest. By enlarging the 

 chest additional room is made, and the air rushes in from 

 the outside to occupy this extra space. Just as in an ac- 

 cordion when it is drawn apart, air streams into it through 

 the various valves made for that purpose. Or, as in the 

 case of a pump, when the piston is lifted, and so additional 

 room made in the pump cylinder, the water under the pres- 

 sure of the atmosphere rushes in to fill this extra space. 

 This enlargement of the chest may occur in three different 

 ways. 



First, it may be enlarged in an up-and-down direction. 

 This is accomplished by the contraction of the muscles of 

 the diaphragm. The diaphragm is a dome-shaped structure 

 with the dome or convexity extending chestward. By the 

 contraction of the muscles in this dome it is pulled down- 

 ward, the dome becomes flattened and the chest cavity en- 

 larged a corresponding amount. 



Second, f he chest may be enlarged by increasing its 

 dimensions in a forward-back direction. This is done by 

 raising the breast bone. By noting the skeleton it may be 



