180 GNATS OR MOSQUITOES — CHAPTER VIII 



mendation to use the castor oil plant to keep a bungalow 

 free from Mosquitoes. I being a sufferer had six plants 

 placed in pots in my rooms. I fancy we must breed a 

 different variety of Mosquitoes than your correspondent, for 

 the castor oil plants are thickly covered with the insects by 

 day, who, at night time, seem to be actually invigorated by 

 the apparently stimulating effect of their new quarters. — D." 



The influence of trees in especial has hitherto been 

 greatly misunderstood. A screen of trees was supposed, in 

 some occult way, to be capable of filtering out malarial 

 germs from the air ; and it is just possible that the presence 

 of a convenient shelter of this sort might in certain cases 

 prevent Mosquitoes wandering further to dwellings which 

 might otherwise have been their nearest convenient refuge ; 

 but it would obviously be bad policy to multiply such 

 shelters. Speaking generally indeed there can be no doubt, 

 that trees greatly favour the multiplication of Mosquitoes. 



This they do in four ways : they afford shelter during 

 the day ; their shade prevents the drying up of puddles ; 

 their flowers often afford the staple food of the insects ; and 

 lastly, they prevent the growth of grass. 



In 1884, the Italian authorities instituted an enquiry as to 

 the influence of disforesting on public health (C. M. p. 141), 

 and the result of their investigations was that they were 

 unable to find any proof that disforesting was injurious to 

 health, but that some facts indicated an opposite effect. 



Popular and professional opinion in India as to the 

 influence of trees on malaria has oscillated, but has gener- 

 ally been in favour of open sites, though no one doubts that 

 trees greatly favour the prevalence of Mosquitoes. 



The history of the large military station of Meean Meer 

 is both curious and instructive in this respect. After the 

 annexation of the Punjab, the large force quartered close to 

 the great native city of Lahore suffered so terribly from 

 malaria that it became absolutely necessary to remove them 

 to some more healthy site. At that time the, as we can 

 now see, perfectly defensible view that open sites are least 

 malarious was that in votrue and the General and his 



