3 20 TEE POPULAR SCIENCE MONTHLY 



peculiar unpleasant crowd odor with which all are familiar. Our sense 

 of smell is subjected continuously to slight stimulation, but it is pecul- 

 iarly and vividly responsive to unpleasant changes in our odorous en- 

 vironment. Thus on entering a crowded, close and stuffy room the odor 

 often seems to us intolerable, and we at once assume that the air is very 

 bad for any one who breathes it. We rush to the window and throw it 

 open, or complain to the janitor, or retreat in disgust. Well, the air 

 may indeed be very bad, but this is not because of its odor, except as to 

 the odor's possible psychic effect. There is a peculiar relation between 

 one's sense of smell and one's esthetic sense, and an unpleasant odor by 

 rudely shocking the esthetic part of our nature may interfere with our 

 efficiency ; but there is no evidence in support of the idea that the odorif- 

 erous elements in crowd air are physically or chemically harmful to us. 

 Our sense of smell, however it may disturb us, is probably the least val- 

 uable of all our senses in contributing to our physical welfare and it 

 can the most readily be dispensed with — a too sensitive nose is really an 

 affliction. This sense is in fact extremely subject to fatigue, and hence 

 on confinement in crowd air our olfactory aversion to it soon ceases — 

 a provision of nature which is not altogether an evil. 



Strangely enough it is only within a period of scarcely more than 

 thirty years that the occurrence and the significance of atmospheric 

 dust have become accurately known. Dust has now been shown to exist 

 in air everywhere : in uninhabited as well as inhabited regions, though 

 the more where man and his works are ; at the tops of lofty mountains ; 

 and over the largest of oceans. The numbers of dust particles found 

 by different observers in a single cubic centimeter of air have varied 

 from 157 at the summit of the Swiss Bieshorn to more than 200,000 

 in a Parisian garden. On dusty streets and within doors, especially in 

 dusty trades, still more dust may exist, and it is estimated that a single 

 puff of tobacco smoke discharges into the atmosphere 4,000,000,000 

 particles. Dust may consist of inorganic and lifeless organic matter, as 

 well as bacteria and other living organisms. It may be carried long 

 distances. The most striking known example of this is the fine pumice 

 which was sent into the air to tremendous heights and in enormous 

 quantities at the time of the extraordinary eruption of the East Indian 

 volcano Krakatoa in 1883. This fine dust was carried completely 

 around the earth and from the extreme north to the extreme south of 

 the largest continents. Moreover, it continued to exist for several years 

 as a component of the earth's atmosphere. To dust particles we owe the 

 existence of clouds, fog and haze, the beautiful colors of the sunset, and 

 in large part the blueness of the sky. Dust is thus our constant com- 

 panion and with every breath we inhale much of it. Our bodies are pre- 

 pared for this and possess defensive agencies for our protection. With 

 these agencies in proper order the greater part of the ordinary inhaled 



