FRESH AIR 319 



rooms, but even here it very rarely reaches four tenths of one per cent., 

 or ten times its usual amount, and this is still well below the harmful 

 limit. It thus appears that carbon dioxide, like oxygen, may be elimi- 

 nated from the problem of fresh air, except under the rarest and most 

 extreme circumstances. 



The amount of carbon dioxide present is often regarded as a con- 

 venient and proper index of the degree of vitiation of air by human 

 beings, and a limit to this is sometimes established by law for factories 

 where many employees work together. Our country unfortunately has 

 not reached that stage of governmental control of its industries in which 

 legal standards of ventilation are established and maintained. We 

 ought to do this in the interests of the health of the workman, but 

 when we are prepared for it we should select some other index of the 

 air's impurity than the amount of carbon dioxide present in it. 



There has long existed a belief — and it has been strengthened by the 

 advocacy of competent men of science — that air that has once been 

 breathed by human beings is poisonous apart from its content in carbon 

 dioxide, and this belief has fixed upon a hypothetical unknown organic 

 constituent, a toxic protein, which is supposed to be produced within 

 the body, volatilized and then cast out with the outgoing breath. Vari- 

 ous attempts have been made during the past twenty-five years to sup- 

 port this belief experimentally. The most of such experiments have 

 consisted in condensing expired air, injecting it into animals and ob- 

 taining symptoms of intoxication. Notwithstanding their seeming con- 

 clusiveness one by one these apparently positive results have been ex- 

 plained on other grounds than as due to the presence of an expired 

 organic poison coming from the lungs and, moreover, they have been 

 offset by more conclusive experiments terminating negatively. The 

 latest of these researches finds no evidence whatever to support the 

 theory of an organic poison, a " crowd poison," as it is sometimes called ; 

 and we must believe that the theory represents one of those erroneous 

 conclusions which science frequently draws from incomplete evidence 

 and then proceeds to utilize in discovering the truth. 



Another feature of vitiated air is odor. Odor is always due to the 

 existence of material, in the form of either gas or very finely divided 

 solid particles, which has the power of stimulating the delicate termi- 

 nals of the olfactory nerves in the walls of the nasal passages. Pure 

 air contains nothing that can stimulate these nerve terminals and there- 

 fore is wholly free from odor. Odor may be introduced into air through 

 decaying organic matter, through illuminating gas or the products of 

 its combustion, through various foreign substances used in industrial 

 procedures, and through emanations from the human body. These last 

 are many and varied, both in quality and origin, and together they give 

 to the air of a crowded assembly which lacks adequate ventilation the 



