264 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



and tlience to infect. It is not transported by the wind — at any rate 

 to a distance — but depends on human movements, on overcrowding, 

 neglected refuse, and absence of proper ventilation. It seems probable, 

 from its persistence on the coast, on the banks of tidal rivers, and on 

 ocean-going ships, that it finds a favorite pabulum in slightly saline 

 deposits. 



DIPHTHERIA. 



Diphtheria, now one of the most fatal maladies of children, both in 

 Europe and America, is equally preventable by purity of air; but since 

 it is commonly caught by infection, and susceptible persons are attacked 

 through slight doses, absolute prevention is difficult. Its propagation 

 depends to a great extent on schools and close aggregations of children, 

 some of whom may be affected by the disease in a mild form, such as 

 slight sore throat. Some cases arise from a disease of the cow, which 

 is not easily identified, but the great majority of cases of the disease 

 are certainly due to the emission into confined air of the microbes from 

 persons already suffering with sore throat or diphtheria, and therefore 

 the great majority of cases would not occur if schools and dwelling 

 houses were well cleansed and ventilated, and if children with sus- 

 pected throats were as far as possible isolated. The gradual growth 

 of diphtheria in villages and towns and its frequent recurrence indi- 

 cate an infection of the air in houses either from a contaminated sur- 

 face soil, from floor or walls, or from the breath of persons who have 

 had the disease and in whose throats the microbe lingers after their 

 recovery. Diphtheria does not occur at all in clean, dry places, unless 

 introduced by some person or imported article carrying the infective 

 organism. The germ is certainly not present in a potent condition in 

 the outer air. Newly inhabited countries and places have always 

 remained free from diphtheria until the germ has been introduced by 

 human agency. 



Diphtheria and scarlet fever are among the most widely and con- 

 stantly prevalent, and most fatal, of all diseases in temperate climates. 

 They are both communicable through the air in proximity to a patient, 

 and this is a very common mode of conveyance. But they have never 

 been known to pass across any considerable space through the outside 

 air. The evidence leads very strongly to the conclusion that they are 

 rarely if ever caught by exposure to infected air which has been very 

 largely diluted in the free atmosphere. Predisposition to diphtheria, 

 and probably to a less extent to scarlet fever, is favored by drain air, 

 sewer air, and the emanations from heaps of decaying animal or vege- 

 table matter, dust heaps, and by the various causes of sore throat. 

 And it is probable that the microbe of diphtheria, which has been iden- 

 tified, frequently infects the surfaces whence the foul emanations pro- 

 ceed. It is certainly present in very many places, especially in houses 

 and localities where the disease has formerly prevailed. Measles are 

 often followed by diphtheria, though no source of infection can be 



