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where the larger mosquitoes of the genus Anopheles 

 abounded. 



He obtained a number of striking coincidences in which 

 these mosquitoes and the disease were confined to the same 

 limited and well-defined regions. He found that Anopheles 

 claviger confines its attacks chiefly to the evening, after 

 sunset ; and in this fact a simple explanation is afforded of 

 the idea that it is dangerous to fall asleep in malarious 

 regions just after sunset. 



Drs. Bignani and Bastianelli, two other Italian workers on 

 this subject, had been trying to infect a person by letting 

 mosquitoes bite him. They attributed their want of 

 success to the use of the wrong kind of mosquito ; and, 

 acting on the advice of Grassi, they obtained some mosquitoes 

 from a malarial district and tried again. 



This time they were successful in infecting the man with 

 malaria of the same type that prevailed in the district from 

 which the mosquitoes came. They came to the conclusion 

 that A . claviger was the most common intermediate host of 

 the parasite of malaria in Italy. Their experiments all 

 pointed to the conclusion that inoculation by the mosquito 

 was the only mode by which infection was acquired ; cer- 

 tainly it was the only method which had been demonstrated 

 experimentally. They traced the development of the cres- 

 centic bodies in the medial intestine of A. claviger after 

 these insects had drawn blood from malarial patients, and 

 also observed later stages of the parasite in the mosquito. 

 The life-history of the parasite is, then, as follows : 



1. Parasites exist as amcebulse within the red blood-cor- 

 puscles of the vertebrate host. They possess the usual 

 power of movement common to this form ; they increase in 

 size, and as they do so, tend to lose their movements and to 

 accumulate in the ectoplasm certain black granules, which 

 are the product of the assimilation of the haemoglobin of the 

 corpuscle. In from one to several days the parasites reach 

 their highest development within the vertebrate host, and 

 become either sporocytes or gametocytes, 



2. The sporocytes, which are produced asexually, contain 

 spores, which vary in number according to the species. They 

 do not possess any appreciable cell wall. When they are 

 mature the red corpuscles which contain them burst, and 

 allow them to fall into the blood-serum. They then attack 

 fresh blood-corpuscles, and continue the propagation of the 

 parasites indefinitely in the vertebrate host. 



3. The gametocytes, on the other hand, while in the blood 



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