ASEXUAL CYCLE IN THE HUMAN SUBJECT 625 



the stomach along with the blood, till the time when it settled 

 in a special form in the salivary glands of the insect. Boss's 

 results were published in 1898. Exactly corresponding stages 

 were afterwards 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. Boss'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. We shall first give a general 

 account of the life-history and then describe the features of the 

 different species. 



The Asexual Cycle in the Human Subject — Schizogony. — 

 With regard to this cycle (Plate V., Fig. 21 a-i), 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 amcebulse or trophozoites within the 

 red corpuscles up to their complete development; schizogony 

 (formerly called sporulation) then occurs. The onset of the ■ 

 febrile attack corresponds with the stage of schizogony and 

 the setting free of the merozoites or enhaemospores, i.e., with 

 the production of a fresh brood of parasites. These soon become 

 attached to, and penetrate into, the interior of the red corpuscles, 

 becoming intra-corpuscular trophozoites ; the cycle is thus com- 

 40 



