CONSUMPTION OF OXYGEN. 419 



which, contains, when inspired, 20-81 parts of oxygen per 

 100, is found on expiration to contain but about 16 parts 

 per 100. In other words, the volume of oxygen absorbed in 

 the lungs is five per cent, or -^j- of the volume of air in- 

 spired. 1 



It is interesting and useful to extend this estimate as far 

 as possible to the quantity of oxygen absorbed in a definite 

 time ; for the regulation of the supply of oxygen where many 

 persons are assembled, as in public buildings, hospitals, 

 etc., is a question of great practical importance. Assuming 

 that the average respirations per minute are 18, and that 

 with each act 20 cubic inches of air are changed, 15 cubic 

 feet of oxygen are consumed in the twenty-four hours, which 

 represents 300 cubic feet of pure air. This is the minimum 

 quantity of air which is actually used, making no allowance 

 for the increase in the intensity of the respiratory processes, 

 which is liable to occur from various causes. To meet all the 

 respiratory exigencies of the system, in hospitals, prisons, etc., 

 it has been found necessary to allow at least 800 cubic feet 

 of air for each person, unless the situation is such that the air 

 is changed with unusual frequency ; for, beside the actual 

 loss of oxygen in the respired air, constant emanations from 

 both the pulmonary and cutaneous surfaces are taking place, 

 which should be removed. In some institutions as much as 

 2,500 cubic feet of air is allowed to each person. 2 



The quantity of oxygen consumed is subject to great 

 variations, depending upon temperature, the condition of the 

 digestive system, muscular activity, etc. The following con- 

 clusions, the results of the observations of Lavoisier and Se- 

 guin, give at a glance the variations from the above-men- 

 tioned causes : 3 



1 MILNE-EDWARDS, Phynohffie, tome ii., p. 510. 



2 TODD and BOWMAN, Physiological Anatomy and Physiology of Man, Phila- 

 delphia, 1857, p. 728. 



3 Taken from LONGET, Traite de Physiologic, Paris, 1861, tome i., p. 526. 

 Though the absolute quantities obtained by Lavoisier and Seguin are not so re- 

 liable as those obtained by later observers, yet the accurate employment of the 



