12 STUDIES IN ADVANCED PHYSIOLOGY. 



about 100 cubic inches as the amount of air which it is im- 

 possible, even by the most violent expiration, to remove. 

 These 100 cubic inches are called the " residual' 7 air. But 

 in ordinary respirations we do not breathe out as much as 

 we can, and under these circumstances there is left in the 

 lung 1,640 centimeters, or 100 cubic inches additional. 

 That is to say, in ordinary breathing there are in the lung 

 at the end of an expiration 200 cubic inches of air. These 

 extra 100 cubic inches are called the "supplemental" air, 

 which, together with the residual air, forms the * 'stationary" 

 air of 200 cubic inches. Now, at an ordinary breath we 

 take in about 500 centimeters, or 30 cubic inches, and of 

 course breathe out the same amount at an ordinary breath. 

 This air is called the "tidal" air. But we are able by a 

 forced inspiration to take in more than we do ordinarily. 

 We seldom breathe as deeply as we can. By a forced in- 

 spiration the lung is able to take in 100 cubic inches more. 

 These extra 100 cubic inches are called the "complemental" 

 air. The amount of air which one is able to breathe from 

 the deepest expiration possible to the deepest inspiration 

 possible is called the "vital capacity." This would then 

 consist of the supplemental air, 100 cubic inches, the tidal 

 air, 30 cubic inches, and the complemental air, 100 cubic 

 inches. In all 230 cubic inches; that is, approximately an 

 even gallon. 



Such determinations of the capacity of the lung, of 

 course with the exception of the residual air, may be easily 

 made by means of the spirometer, an instrument found in 

 almost every well-equipped gymnasium. 



4. The Amount of Air Used. In the mechanics of res- 

 piration there have been considered so far the following 

 topics: 1. The movements of respiration, or those changes 

 by means of which the capacity of the chest is enlarged and 

 contracted, and so the air drawn into it or forced out. 2. 

 The rate of these movements. 3. The capacity of the 

 average lung. A very important topic in the mechanics of 

 breathing still remains to be answered. It is the question 



