THE PENRYN CRUSADE 95 



A rain on October 10th, nth, and 12th washed out 

 old pools and was followed by warm weather, which 

 dried up the greater part of the pools. It was therefore 

 unnecessary to do much oiling, and the greater part of 

 the remaining time in October was devoted to getting 

 together the material for this report, and working it 

 up. 



The Problem at Penryn. — Previous to the introduc- 

 tion of irrigation water it is certain that malaria 

 was not endemic. The natural drainage is excellent, 

 and the long, warm summers dry up in a very short 

 time any pools left by the spring rains, thus giving the 

 mosquitoes little chance to breed. Whether Anopheles 

 were present before irrigation was introduced is not 

 known, but the mosquito has certainly been present 

 since, being imported probably from the valley region. 

 It is easy to conceive of a person with malarial parasites 

 in his blood coming into this region after the introduc- 

 tion of Anopheles, and from this person the Anophe- 

 line mosquitoes becoming infected, and in turn inoculat- 

 ing other persons, the disease then becoming endemic. 

 This can only occur where conditions are favorable 

 to mosquitoes, and implies the presence of standing 

 water during a large portion of the year. 



Owing to the good natural drainage and the dry 

 summer weather, the presence of pools and marshes 

 in summer is an unnatural condition, and can be ex- 

 plained only by improper use of irrigation water. 

 Irrigation should always be accompanied by provision 



