COLD AND COLDS 



appears that it depends on what age group you take. If you take 

 small children, you will find .that the rare influenza viruses 

 produce quite a lot of infection. In any age group, the respira- 

 tory syncytial virus may be prevalent in one year, and in another 

 year it may be completely absent. Rhinoviruses seem to be the 

 hard core which cause more colds than anything else, but I should 

 make it clear that there are still a great many colds from which 

 we havn't been able to cultivate any viruses, although these 

 things will still produce colds in volunteers. So there is still 

 quite a lot to learn, but I think the proportion of the colds caused 

 by different agents probably varies very much from time to 

 time and from place to place. 



Well, I don't know that anybody has actually solved all my 

 more difficult problems for me, but anyway, I am very grate- 

 ful for all the suggestions that have been made in the matter. 



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