410 THE COMPOSITION OF EXPIRED AIR. 



the persons who breathe it is due to the greater number of pathogenic 

 microorganisms in such localities. It is quite possible that such im- 

 pure atmospheres may affect the vitality and the bactericidal powers 

 of the cells and fluids of the upper air passages with which they come 

 in contact, and may thus predispose to infections, the potential causes 

 of which are almost everywhere present, and especially in the upper air 

 passages and in the alimentary canal of even the healthiest persons, 

 but of this we have as yet no scientific evidence. It is very desirable 

 that researches should be made on this point. 



10. The discomfort produced by crowded, ill ventilated rooms in per- 

 sons not accustomed to them is not due to the excess of carbonic acid, 

 nor to bacteria, nor, in most cases, to dusts of any kind. The two 

 great causes of such discomfort, though not the only ones, are exces- 

 sive temperature and unpleasant odors. Such rooms as those referred 

 to are generally overheated, the bodies of the occupants and, at night, 

 the usual means of illumination contributing to this result. 



The cause of the unpleasant, musty odor which is perceptible to most 

 persons on. passing from the outer air into a crowded, unventilated room 

 is unknown ; it may, in part, be due to volatile products of decomposi- 

 tion contained in the expired air of persons having decayed teeth, foul 

 mouths, or certain disorders of the digestive apparatus, and it is due, 

 in part, to volatile fatty acids given off with, or produced from, the 

 excretions of the skin, and from clothing soiled with such excretions. 

 It may produce nausea and other disagreeable sensations in specially 

 susceptible persons, but most men soon become accustomed to it, and 

 cease to notice it, as they will do with regard to the odor of a smoking 

 car, or of a soap factory, after they have been for some time in the place. 

 The direct and indirect effects of odors of various kinds upon the com- 

 fort, and perhaps also upon the health, of men are more considerable 

 than would be indicated by any tests now known for determining the 

 nature and quantity of the matters which give rise to them. The 

 remarks of Eenk (32, p. 174) upon this point merit consideration. Cases 

 of fainting in crowded rooms usually occur in women, and are connected 

 with defective respiratory action due to tight lacing or other causes. 



Other causes of discomfort in rooms heated by furnaces or by steam 

 are excessive dryness of the air, and the presence of small quantities 

 of carbonic oxide, of illuminating gas, or of arsenic derived from the 

 coal used for heating. 



11. The results of this investigation, taken in connection with the 

 results of other recent researches summarized in this report, indicate 

 that some of the theories upon which modern systems of ventilation 

 are based are either without foundation or doubtful, and that the prob- 

 lem of securing comfort and health in inhabited rooms requires the 

 consideration of the best methods of preventing or disposing of dusts 

 of various kinds, of properly regulating temperature and moisture, 



