276 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



of a typhoid case does not appear to convey the disease, apart from 

 excreniental matter exposed to the air. Yellow fever seems to grow in 

 conditions somewhat resembling those which are favorable to cholera — 

 filthy, damp surfaces in great heat — and infects the air in the neighbor- 

 hood of its growth, especially banks of rivers, harbors, holds and bilges 

 of ships, and dirty, dark, crowded streets. It sometimes infects direct 

 from a patient. These three saprophytic or semisaprophytic diseases 

 may be supposed to be propagated a short distance from place to place 

 through the air without the intervention of a human subject, but have 

 neverbeen known to be carried far independently of human transporting 

 agency. 



(3) Diseases which arise from deposits of organic matter from the 

 lungs and skin, and also probably from other excrementitious filth. 

 Typhus and the plague may be named in this class, but other condi- 

 tions of filth are powerful in their genesis. Plague is both miasmatic 

 and contagious, and, where concentrated, seems to be capable of pass- 

 ing through several hundreds of yards of air. Prolonged breathing 

 of the sick-room air both in plague and typhus is the most effectual 

 means of infection. Damp, alluvial soils; streets, walls, and floors 

 with damp organic deposits sticking to them; carcasses and refuse 

 lying unburied around houses; in these situations the plague fungus 

 flourishes. Diphtheria arises probably from somewhat similar breed- 

 ing x>laces, from heaps of house refuse, from middens, drains, ash 

 heaps, and polluted ground, floor, and walls, and is transmitted a short 

 distance through the air, probably seldom more than 10 or 20 yards. 

 It is very often, probably in the majority of cases, carried by the air 

 from person to person through a short distance, most easily in damp, 

 close, or confined air, like so many other infections. The diphtheria 

 fungus, when it has been once introduced, sticks to certain places, damp 

 houses and damp organically polluted sandy soil seem to favor it. It 

 is improbable that it is ever conveyed far from place to place through 

 the air to persons except by human agency and the movements of 

 domestic animals. Pneumonia may possibly depend on somewhat sim- 

 ilar conditions, and may be caught by one person from another through 

 the air. Consumption, phthisis, or tuberculosis, depends to a very great 

 extent on conditions similar to those of typhus, and is spread through 

 the air a short distance in the dried matter of saliva and sputum. 



(4) Scarlet fever, measles, whooping cough, influenza, and dengue 

 arise from conditions outside the body which are unknown, but decay- 

 ing organic matter may provisionally be assumed to have been their 

 original breeding ground. They are now almost entirely dependent 

 on transmission from person to person, and to a very large extent on 

 transmission through a short distance of air. It is very seldom that 

 these maladies are caught in the open air, so that the medium of trans- 

 mission is the confined and more or less foul air of schools, houses, 

 churches, and theaters. They are never caught in isolated positions in 



