ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 271 



are still warm and the air is rapidly cooling. When the microbes are 

 dense in the humid and misty low stratum of air, and when the human 

 body is being quickly chilled, they are able to attack successfully. The 

 microbe is probably a very common and widely diffused one, and may 

 be present in comparatively small proportion and in less vigor in the 

 lower air generally over the land. At sea it would be absent, and indeed 

 there is good evidence that it does not bear long transport in a virulent 

 state in the free air. Colds are scarcely ever caught on the open sea, 

 even if the clothes be wet with salt water, and breezes straight from the 

 Atlantic do not seem capable of inducing sore throat or cold. But, of 

 course, to make an experiment crucial, previous life in the open air, 

 disinfection of clothes and if possible of the breathing organs, would 

 be necessary. It is not improbable that the microbe of colds, like that 

 of pneumonia, may be frequently present in the mouth. The experience 

 of St. Kilda, 1 which used to be absolutely free from colds until the 

 annual boat arrived from the mainland, points to the ordinary presence 

 of the infective particles on clothes or in the breath. The islanders 

 were nearly all struck down with severe colds within a day or two after 

 welcoming their visitors. Probably a similar dose of infection would 

 be quite insufficient to prostrate persons on the mainland who were 

 accustomed to the petty assaults of the microbe, and protected by 

 scarcely noticed symptoms of catarrh. 



An exactly similar thing occurs in the case of influenza. Hundreds 

 of instances were observed in which the proximity of persons who had 

 had influenza or had been near cases of influenza gave it to others, and 

 often persons lately arrived in a place which had passed through the 

 epidemic were struck down while the great majority of the resident 

 population remained protected, at least for some months. 



Colds protect against their own recurrence in most people for some 

 months. Severe colds go through a house after the manner of an infec- 

 tious disease, and can be similarly guarded against by isolation. The 

 air certainly conveys a cold for several feet through confined air, and 

 in a, closed railway carriage susceptible persons 'who have been free 

 from colds for some time are easily infected. An attack is often attrib- 

 uted to a chill felt at the beginning of the infliction, but in reality the 

 cold has usually been caught some hours or a day or two before, and 

 the feeling of chill is simply the beginning of the disorder, as in other 

 infectious maladies. On the other hand, there may be a real chill, 

 which gives opportunity to the microbe to make its attack and produce 

 a feverish cold in a day or two. Foul air and crowded rooms are emi- 

 nently conducive, especially if combined with drafts, to disseminate 

 colds. 



Persons arriving in town from the pure air of the country or from a 

 sea voyage are very apt to catch cold. They have been living apart 



1 And other islands. See Darwin's "Naturalist's Voyage." Report of the Local 

 Government Board; Epidemic Influenza, London. 



