COLD AND COLDS 



viruses). They can be grown in cultures of human embryonic kidney, 

 and in diploid cell lines from human embryonic lung; a minority of 

 the strains grow also in monkey kidney and other primate cells .The 

 trick is to cultivate at a lower temperature than is conventional 

 (33'-' C), at a lower pH, and in rolled tubes to give good oxygenation. 

 New developments make their study easier. They grow in a wider 

 range of cells ; they can be studied quantitatively by counting the 

 tiny foci of degeneration produced in cell sheets (Parsons and Tyr- 

 rell, 1961) ; even macroscopically visible plaques can now be pro- 

 duced (Porterfield, 1962). These Rhinoviruses resemble entero- 

 viruses in being very small, ether- resistant viruses. They differ in 

 their cultural requirements, greater lability towards acid, habitat, 

 and pathogenicity. They are of many different serological types, "and 

 although we don't yet know how many, 30 is probably a low estimate. 

 We are now passing the preliminary stage of establishing that these 

 viruses do, in fact, cause many colds all over the world. The tech- 

 niques developed can now be applied to studies of epidemiology. 

 Quantitative studies are particularly needed. For many years in our 

 work at Salisbury we could only detect virus by seeing whether or 

 not material under study would produce colds when dropped up the 

 noses of volunteers. Our subjects reacted very variously, and at 

 best we could only infect 50 per cent of them. Quantitative studies 

 were almost impossible. Now that one can count rhinovirus plaques, 

 things are very different. It should not be difficult to discover the 

 whereabouts of virus in the environment, and just when, how, and in 

 what quantity it is shed from an infected person. I should not be 

 wholly surprised to discover that virus shed by a cold-sufferer in 

 summer wasquantitatively less than in winter, so that there was less 

 danger of infecting others. All sorts of other quantitative studies 

 should be applicable from now on, including those concerned with 

 seasonal variation in resistance to colds. 



Resistance to Colds 



Jackson and Dowling (19 59) in Chicago produced evidence that 

 resistance to five strains of colds was specific, directed against 

 a particular strainofvirus.Discovery of the serological multiplicity 

 of cold viruses fits in with this. Antibodies to particular strains 

 seem to be well correlated with resistance to those strains. Yet other 



307 



