522 MALARIAL FEVER 



In birds affected with this organism, he was able to trace all 

 stages of its development, from the time it entered the stomach 

 along with the blood, till the time when it settled in a special 

 form in the salivary glands of the insect. Ross's results were 

 published in 1898. Exactly corresponding stages were after- 

 wards found in the case of the different species of the human 

 parasite, by Grassi, Bignami, and Bastianelli ; and these with 

 other Italian observers also supplied important information 

 regarding the transmission of the disease by infected mosquitoes. 

 Abundant additional observations, with confirmatory results, 

 were supplied by Koch, Daniels, Christophers, Stephens, and 

 others. Wherever malaria has been studied the result has been 

 the same. Lastly, we may mention the striking experiment 

 carried out by Manson by means of mosquitoes fed on the blood 

 of patients in Italy suffering from mild tertian fever. The 

 insects, after being thus fed, were taken to London and allowed 

 to bite the human subject, Manson's son, Dr. P. Thurburn 

 Manson, offering himself for the purpose. The result was that 

 infection occurred ; the parasites appeared in the blood, and 

 were associated with an attack of tertian fever. Ross's discovery 

 has not only been a means of elucidating the mode of infection, 

 but, as will be shown below, has also supplied the means of 

 successfully combating the disease. 



From the zoological point of view the mosquito is regarded 

 as the definitive host of the parasite, the human subject as the 

 intermediate host. But in describing the life history, it will be 

 convenient to consider, first, the cycle in the human body, and, 

 secondly, that in the mosquito. Various terms have been 

 applied to the various stages, but we shall give those now 

 generally used. 



The Cycle in the Human Subject. With regard to this 

 cycle, it may be stated that the parasite is conveyed by the bite 

 of the mosquito in the form of a small filamentous cell 

 sporozoite or exotospore, which penetrates a red corpuscle and 

 becomes a small amoeboid organism or amoebula. There is then 

 a regularly repeated asexual cycle of the parasite in the blood, 

 the length of which cycle determines the type of the fever. 

 During this cycle there is a growth of the amcebulae or 

 trophozoites within the red corpuscles up to their complete 

 development ; sporulation or schizogony then occurs. The onset 

 of the febrile attack corresponds with the stage of sporulation 

 and the. setting free of the spores (enhsemospores or merozoites), 

 i.e. with the production of a fresh brood of parasites. These 

 spores soon become attached to, and penetrate into the interior 



