30 
already seen, expired air is saturated, or nearly so, with moisture. The 
quantity thrown off from the lungs daily is subject to variation, but is 
usually between 9 and 10 ounces. 
EFFECTS OF VITIATED AIR ON HEALTH. 
I have already pointed out that vitiated air, and more particularly 
air that has received largely the products of respiration, is extremely 
deleterious to health. But I would now emphasize the insidious 
character of these impurities, how they gradually undermine the health 
and how easy it is for us to habituate ourselves to a morbid condition 
of the air we breathe. Fainting fits, giddiness, nausea, and headache 
are recognized as the immediate results of breathing the air of badly 
ventilated halls and rooms, but it is not so widely known that indiges- 
tion, diarrhoea, and impaired and feeble condition of the system a 
general lowering of the bodily and mental vigour are often caused by 
the continuous breathing of vitiated air. Those who through careless- 
ness, or apparent necessity of circumstances, live and work in a con- 
fined atmosphere, run a great risk, for apart from immediate evil results, 
they are not in a condition to resist attacks of zymotic diseases. 
Further, statistics clearly prove that the death rate of those living and 
working in an impure atmosphere (e.g*. certain factories, mines, crowded 
tenement houses, etc.), is much higher than amongst those whose more 
fortunate lot allows them to live and work in a purer air. 
VENTILATION. 
For private dwellings no cheap and efficient system of artificial 
ventilation has as yet been invented. For public halls, schools, hos- 
pitals, and the like, however, there are now systems by which the air 
may be kept perfectly wholesome without creating a draft, either in 
summer or winter, and at the proper degree of temperature and mois- 
ture. What we might call public ventilation should now become a 
matter for legislation. Our public schools, halis of assembly, and all 
confined, spaces, where large numbers of people congregate, should all 
be provided with the requisite means for constantly renewing the air. 
As private individuals, we have to be thankful that the materials of 
which our houses are constructed and more especially brick and 
plaster are porous, allowing a constant interchange of the air 
within with that outside. We should take care to increase this 
