xv STRUGGLE WITH DISEASE 185 



Therefore, one party said that it was the damp 

 which caused mildew, just as until lately people 

 said that damp caused ague and marsh fever and 

 malaria. We know now that these diseases are 

 caused not by the damp, but by a minute organism 

 which is carried from one person to another by 

 mosquitoes, and that mildew is due to a fungus. 



But in Pliny's time, in addition to the people 

 who reasoned sufficiently to see that there was 

 some connection between damp and mildew, there 

 were other people who did not reason at all. They 

 saw that mildew appeared in their crops in spring- 

 time, and they looked for the cause, not on the 

 earth, but in the changes which were taking place 

 in the sky at this season. To please these people 

 Pliny gave instructions about the crabs and the 

 young dog. 



Let us take a long jump in time from Pliny 

 and come down to the nineteenth century. In a 

 little book published in 1846 (not so very long 

 ago !) we read that blight and mildew have " three 

 distinct and dissimilar causes." These are " cold 

 and frosty winds, sultry and pestilential vapours, 

 and the propagation of a parasitical fungus." The 

 difference from Pliny's statements is not so great 

 as it seems at first sight. This author adds a 

 fungus as a cause, but he mentions that last. He 

 does not tell us where the sultry and pestilential 



