o'SHEA A8PECTS OF MENTAL ECONOMY. 153 



CHAPTER VIII. 



FRESH AIR, EXERCISE AND REST IN THE PRODUCTION AND 

 EXPENDITURE OF CEREBRAL ENERGY. 



§1. Function of Oxygen in {he Organism, — Many people 

 seem to think that albumen, fat, and carbohydrates are suffi- 

 cient in themselves to supply the organism with energy; if you 

 eat enough, they say. you will be vigorous enough in mind and 

 bodv. But a little reflection will teach one that fat and carbo- 



1/ 



hydrates as such are only force in potentia, so to speak. They 

 are absolutely powerless in the system until they are oxydized, 

 so that an adequate supply of oxygen is as essential to proper 

 nutrition, in the broad sense, as a liberal quantity of carbohy- 

 drates and other substances. An organism deprived of a due 

 allowance of oxygen becomes lethargic; and if it be altogether 

 cut off, entire absence of action supervenes, a fact with which 

 everyone is of course familiar. 



Now, observation and experiment have indicated somewhere 

 near the amount of oxygen which the human body requires for 

 greatest efficiency, and this must be secured by a constant ap- 

 portionment of air containing the "life giving element" in a 

 certain uniform proportion. In determining this proportion 

 the ratio of C0 2 to the other constituents of an atmosphere is 

 .usually taken as an index of the purity of that atmosphere, 

 since this gas is generally found in the presence of other gases 

 which, vitiate the air. It has been calculated that more than 

 4 parts of carbonic acid gas in 10,000 parts of air renders the 

 latter incapable of furnishing oxygen to the system in the re- 

 quired quantities. 1 This estimate can be only relatively true, 

 however, since organisms differ respecting the amount of oxy- 

 gen which they need to support mental and bodily activities. A 



1 For the results of investigations relating to this subject, see Burnham, Peda- 

 gogical Seminary, June, 1892, p. 23, et seq. 



