Mosquitoes and Malaria 113 



correctness of this theory, and his continuous in- 

 defatigable labors in trying to demonstrate it. It 

 was an important piece of scientific work, and 

 shows what a man can do even when the obstacles 

 seem insurmountable. 



THE PARASITE IN THE MOSQUITO 



Briefly stated again, the problem was this: We 

 have here a parasite in the blood which behaves as 

 do many other forms of life. Some of these para- 

 sites do not go on with their development until 

 they are removed from the circulation. Now, how 

 are they thus removed from the circulation under 

 normal conditions ? This must first be solved be- 

 fore the still greater and more important problem 

 of how the parasite gets from one human host to 

 another can be taken up. In studying this over 

 Manson reasoned that certain suctorial insects were 

 the agencies through which blood was most com- 

 monly removed from the circulation and he ven- 

 tured the guess that this change in the parasite 

 that may be seen taking place on the slide under 

 the microscope, normally takes place in the stom- 

 ach of some insect that sucks man's blood. Ross 

 was greatly impressed with the theory and began 

 his long and apparently hopeless task of finding 

 these parasites in the stomach of some insect. 



