PLASMODIA 291 



yet according to the rules of zoological nomenclature the first 

 given name must be retained. 



In 1896 Ross found, while studying a form of malaria affecting 

 birds, that the parasite was transmitted from infected to healthy 

 birds by the bite of the common mosquito, Culex. Reasoning 

 from this fact, he concluded that the malarial parasite giving rise 

 to the disease in human beings might be conveyed in a similar 

 manner. After a long series of experiments he found that the 

 latter could not develop in the body of Culex, but that it did develop 

 in another variety, Anopheles. He observed rounded, pigmented 

 bodies in the stomach wall of Anopheles that had been fed with 

 the blood of malarial patients, and he was able to trace all the 

 stages of development from the time the organism entered the 

 stomach with the blood until it settled in the poison-salivary gland 

 of the insect ready to be transferred again to a human host. 



Strikingly conclusive evidence of the ability of mosquitoes 

 to transmit infection was afforded by Manson in London. About 

 forty mosquitoes were shipped from Rome after sucking blood 

 from a case of tertian malaria, and Hanson's son allowed himself 

 to be bitten by them, with the result that an attack of tertian fever 

 followed and the parasites were found in the patient's blood. 



Reproduction. Both man and mosquito are necessary to 

 complete the life cycle of the parasite. Since the sexual phase is 

 passed within the mosquito the latter is considered the definitive 

 host and the former the intermediate host. It is, however, more 

 convenient to consider the asexual cycle first. 



Asexual Phase (Schizogony). At the time the parasite is 

 conveyed by the bite of the mosquito it appears as a small ring- 

 like body, and on entering the blood stream of its human host 

 it attaches itself at once to a red blood corpuscle and commences 

 to send out distinct pseudopodia into the cell substance. As it 

 approaches maturity segmentation begins, giving to it the appear- 

 ance of a rosette within the corpuscle. Very soon the segments 

 separate into small, rounded forms or merozoites, the cell wall of 

 the red blood corpuscle ruptures, and the young merozoites thus 

 liberated into the blood stream at once fasten themselves on to 



