xv STEUGGLE WITH DISEASE 189 



of those insignificant black or rust-coloured stripes 

 which occur on the leaves of corn and other 

 grasses ? 



We must remember also to include in our 

 gratitude not only the individual people who have 

 worked at this particular subject, but all the 

 innumerable people who, quite often without in- 

 tending it, have made the work of the others 

 possible. The opticians who worked at improving 

 microscopes, the chemists who made the dyes, we 

 have already mentioned, but these are only two sets 

 of people ; it took a great number of other workers 

 before the exact cause of rust in wheat could be 

 explained. 



Even yet there is still a great deal to be done, 

 for it is not possible to prescribe a cure, though 

 it is possible to suggest ways of diminishing the 

 risk of infection. But it is clear, is it not, that 

 knowledge does not come merely with the lapse of 

 time ? We haye seen that for 1800 years after 

 Pliny not much progress was made. Progress 

 comes when in a community there are a number of 

 men, with different types of mind, who are willing 

 to devote themselves to the search for knowledge. 

 Each may only succeed in doing very little, but the 

 next generation can stand on the platform they 

 have built, and so rise to heights they never 

 dreamt of. 



