ANDREWES 



physiological adjustments which follow a fall in temperature? Most 

 people not infrequently get wet feet or sit in draughts without feeling 

 chilly and without a subsequent cold; these incidents they forget, 



I must digress before putting forward my third explanation. There 

 is evidence as regards several respiratory virus infections, and 

 more particularly influenza, that virus may be widely seeded into a 

 population and yet not give rise to an immediate epidemic. Something 

 has to be right before the outbreak can get started. Particularly re- 

 markable was the way in which the A2, commonly called Asian in- 

 fluenza, spread rapidly in tropical countries, yet was seeded fairly 

 freely into North America and Europe some months before anything 

 very much happened there. With onset of cooler weather, the epi- 

 demic broke out. Common cold viruses have occasionallybeen iso- 

 lated from normal noses and it is not unlikely that in some people 

 they, like some other viruses, may be in a state of unstable equi- 

 librium with their host, awaiting activation by an appropriate stim- 

 ulus. We may not have induced in any of our comparatively few 

 volunteers the right kind of equilibrium with the virus we gave them; 

 it may be only a small percentage of the population in which chilling 

 would upset a balance and unleash a cold. 



One thing seems fairly certain. In small isolated communities in 

 the Arctic, Antarctic, or elsewhere, cold viruses are lost or else 

 the members of the small community soon become immune to the 

 viruses circulating amongst them (Paul and Freese, 1933), Chilling 

 does not induce colds in them unless there is some contact with the 

 outside world which could possibly introduce fresh viruses. Many of 

 you will be able to tell me if I am misinformed in this matter. 



Season and Outbreaks of Colds 



Let us now turn to cold and its effects on the incidence of colds 

 in large populations. Every chart I have seen tells the same story: 

 colds are much more frequent in winter than in summer. One obser- 

 ver (Lederer, 1928) asserts that summer colds are more often 

 sporadic and not associated with other cases in the family. In the 

 Northern Hemisphere there is commonly a peak in the incidence of 

 colds with the onset of cooler weather in September and October, a 



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