DUST AND AIR POLLUTION 81 



suitable nidus for putrefactive bacteria. The large quantities of 

 bacteria which a decayed tooth contains are easily demonstrated. 



From the two series of experiments which we have now con- 

 sidered we may gather the following facts ! — 



{a) That air may contain great numbers of bacteria which may 

 be readily inspired. 



(&) That in health those inspired do not, as a rule, pass beyond the 

 moist surface of the nasal and buccal cavities, except in persons who 

 practice oral instead of nasal respiration. 



(c) That in the nose and mouth there are various influences of a 

 bactericidal nature at work in defence of the individual. 



(d) That expired air in normal qxiiet breathing contains, as a 

 rule, no bacteria whatever. 



The practical application of these things is a simple one. To 

 keep air free from bacteria, the surroundings must be moist. Strong 

 acids and disinfectants are not required. Moisture alone will be 

 effectual. Two or three examples at once occur to the mind. 

 Anthrax spores are conveyed from time to time from dried infected 

 hides and skins to the hands or bodies of workers in warehouses in 

 Bradford, Bermondsey, Finsbury, and other places. If the surround- 

 ings are moist and the hides moist, anthrax spores and other bacteria 

 do not remain free in the air. As a matter of actual experience, it has 

 been found that handling dried hair or dried skins leads to more anthrax 

 infection than handling the same articles in a moist condition.* 



Again, the bacilli (or " spores ") of tuberculosis present in sputum 

 in great abundance cannot infect the air until and unless the 

 sputum dries. So long as the expectorated matter remains on the 

 pavement or handkerchief wet, the surrounding air will derive from 

 it no bacilli of tubercle. But when in the course of time the sputum 

 dries, then the least current of air will at once infect itself with the 

 dried spores or bacilli. It should, however, be remembered that the 

 " cough-spray " and microscopic particles of saliva emitted in shout- 

 ing, heavy breathing through the mouth, etc., have been shown by 

 Flligge and others to carry the bacilli of tubercle. Such conveyance 

 may, of course, prove a channel of infection between diseased and 

 healthy persons. The typhoid hacillus, too, occupies the same position. 

 Only when the excrement dries can the contained bacteria infect 

 the air. It is of course well known that the common channel of 

 infection in typhoid fever is, not the air, whereas the reverse holds 

 true of tuberculosis. But if it happens that the excrement of 

 patients suffering from typhoid dries, the air may become infected ; 

 if, on the other hand, it passes in a moist state into the sewer, even 

 though untreated with disinfectants, all will be well as regards the 

 surrounding air. 

 * Annual Reports of Medical Inspector of Factories and Workshops, 1902 and 1903. 



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