Mosquitoes and Malaria 115 



was able to give a complete life-history of this 

 parasite. His experiments have been repeated 

 many times, and the conclusions he arrived at are 

 as undeniable as any of the known facts of science. 



The whole life-history as we now know it can 

 be summed up as follows: The parasites develop 

 within the circulation but certain of them seem to 

 wander about and do not go on with their devel- 

 opment there. When these particular parasites are 

 taken into the stomach of most mosquitoes they 

 are digested with the rest of the blood. But when 

 they are taken into the stomach of a mosquito 

 belonging to the genus Anopheles or other closely 

 related genera they are not digested but go on with 

 their development, conjugation and fertilization 

 taking place, resulting in a more elongated form 

 which makes its way through the walls of the stom- 

 ach on the outside of which are formed the little 

 nodules discovered by Ross on his mosquitoes. 

 Within these nodules further division and develop- 

 ment takes place until finally the nodule is burst 

 open and many thousand minute rod-like organ- 

 isms, sporozoites, are turned loose into the body- 

 cavity of the mosquito. Owing to some unknown 

 cause these little organisms are gathered together 

 in the large vacuolated cells of the salivary glands 

 of the mosquito, and when the mosquito bites a 



