PUBLIC HEALTH 7 



The protozoan blood parasites that cause malaria were first 

 demonstrated many years ago, in 1880, by a French surgeon, 

 Laveran, who discovered them in the blood of persons suffer- 

 ing from malaria. Five years later an Italian, Golgi, dis- 

 tinguished three kinds, each associated with one of the more 

 familiar types of malaria. They were found to go through a 

 regular life cycle in the red blood corpuscles and, from anal- 

 ogy with other known Protozoa, it was suspected that in 

 addition to their non-sexual generations in the human blood 

 there must be a sexual development in some cold-blooded 

 animal. Manson was led to suspect that some insect might 

 be the secondary host and, working on this hypothesis, Ross 

 in India first found the malarial parasites in a certain kind of 

 mosquito in 1898. He had worked for nearly three years on 

 a common mosquito belonging to the genus Culex without 

 result, but finally in a mosquito of the genus Anopheles was 

 able to trace the development of the parasite. His epoch- 

 making discovery has been since amply confirmed and ex- 

 tended by experimental proof till we now know that the 

 various types of malarial blood parasites complete their life- 

 cycles in anopheline mosquitoes, the latter acting as the 

 sole carriers of the disease. 



The details of growth and development of these parasites, 

 which belong to the Protozoan genus Plasmodium, are ex- 

 tremely interesting, but far too complicated to discuss briefly. 

 In general it may be said that the blood of persons suffering 

 from malaria contains the parasitic organisms, and that these, 

 on being taken into the stomach of the proper kind of mos- 

 quito, undergo certain changes and later penetrate the wall 

 of the stomach to form vesicular swellings. Within these 

 they multiply, and finally on the bursting of the nodule are 

 set free in the body cavity and find their way to the salivary 

 glands. After becoming infected, a period of twelve to twenty 

 days is required for these changes in the mosquito. Then for 

 a period of several weeks the virulent organisms remain in 

 the salivary glands and if the mosquito bites a second person 

 the parasites are introduced with the salivary secretion, 



