20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 63 



and activity. If there is constant cooling by ventilation, then a per- 

 son is kept more active and the general health is improved. 

 As Dr. M. J. Rosenau said in his recent address : 



Thus our entire conception of ventilation has changed, owing to the fact 

 that we now do not believe that fresh air is particularly necessary in order 

 to furnish us with more oxygen or to remove the slight excess of carbon 

 dioxide. It is plain that it is heat stagnation that makes us feel so uncom- 

 fortable in a poorly ventilated room rather than any change in the chemical 

 composition of the air. It has been made perfectly clear from the work 

 of Fliigge that one of the chief functions of fresh air is to help our heat-regu- 

 lating mechanism maintain the normal temperature of the body. It is 

 necessary to have some 2,000 to 3,000 cubic feet of air an hour to maintain 

 our thermic equilibrium — just the amount that was formerly stated to be 

 necessary to dilute the carbon dioxide and supply fresh oxygen. The prac- 

 tice of ventilation, therefore, has not altered so much as has our reason for 

 attaching importance to clean, cool, moving air, which has completely changed.' 



The foregoing resume is perhaps not complete without mentioning 

 the recent work of Prof. Yandell Henderson, of Yale University, 

 who has brought forward his " Acapnia " theory (acapnia meaning 

 diminished carbon dioxide in the blood) . He says :' 



We have really at the present time no adequate scientific explanation for 

 the health-stimulating properties of fresh air and the health-destroying influ- 

 ence of bad ventilation. . . . The subject needs investigating along new lines 

 rather than a rehearsal of old data. 



Dr. Crowder's recent experiments ' also furnish additional evidence 

 against the theory that efficient ventilation consists in the chemical 

 purity of the air, in its freedom from " a toxic organic substance." 

 Even were a poisonous protein substance present in the expired air 

 — a fact no experimenter has yet been able to demonstrate — the 

 human organism under every-day conditions is apparently well able 

 to adjust itself to the reinhalation of this hypothetic substance, since 

 a considerable quantity of the expired air is always taken back into 

 the lungs." 



We consider that experiments like these demonstrate most valu- 

 able and practical truths and that is our excuse for introducing 

 them so particularly in this place. When we consider that the aver- 

 age man exhales from 9,000 to 10,800 liters of air in twenty- four 



' Boston Medical and Surgical Journal, Nov. 6, 1913. 



' Trans. Fifteenth International Congress on Hygiene and Demography, 

 Vol. 7, p. 622. 



* Crowder, Thomas R. : The Reinspiration of Expired Air (Arch. Int. Med., 

 October, 1913, p. 420). 



* Editorial in Journ. Amer. Med. Ass., Nov. 29, 1913. See also page 108. 



