ii 4 



Insects and Disease 



When we remember that they are so minute that 

 they can only be seen by the use of the highest 

 power of the microscope we can realize something 

 of the magnitude of the task. Ross, who was at 

 that time stationed in India, selected the mosquito 

 as the most likely of the insects to be the host that 

 he was looking for. For over two and one-half 

 years he worked with entirely negative results, for 

 after examining thoroughly many thousands of 

 mosquitoes he found no trace of the parasite. 



Practically all his work was done on the most 

 common mosquito of the region, a species of Culex. 

 But one day a friend sent him a different mosquito, 

 one with spotted wings, and in examining it he 

 was interested to note certain oval or round nodules 

 on the outer walls of the stomach. On closer ex- 

 aminations he found that each of these nodules con- 

 tained a few granules of the coal-black melanin of 

 malarial fever. Further studies and experiments 

 showed that these particular cells could always be 

 found in the walls of the stomach of this particular 

 species of mosquito a few days after it had bitten 

 a malarial patient. This epoch-making discovery 

 was made in 1898. Ross was detailed by the Eng- 

 lish government to devote his whole time to the 

 further solution of the problem, and after two 

 years more of careful experimentation and study 



