Malarial Parasites 527 



ered that all mosquitoes are not equally susceptible of infec- 

 tion, and, therefore, not all able to spread the infection. 

 Indeed, he so carefully studied the mosquitoes as to narrow 

 the infectability and infectivity of mosquitoes down to one 

 single family, the Anophelinae, and to one single genus, 

 Anopheles. 



There remained, however, one more important fact to be 

 elucidated, and one more mysterious body to be accounted 

 for, viz., the " flagellated " body that had misled Manson. 

 This was found by MacCallum* to be but the spermatozoit 

 of the male parasite. While observing one of the malarial 

 parasites of birds Plasmodium danliewskyi he saw one of 

 these " flagella " swimming away from its parent parasite, and 

 followed it carefully, moving the slide upon the stage of the 

 microscope. It, and others of its kind, approached a large 

 globular parasite, to which one effected an attachment and 

 into which it entered. MacCallum realized that he had 

 observed the sexual fertilization of the organism. Thus 

 from its time-honored place as the typical miasmatic disease, 

 full of mystery and obscurity, malarial fever suddenly had 

 a flood of light thrown upon it by which every peculiarity was 

 fully illuminated. 



In summarizing the knowledge thus set forth we find the 

 following facts : 



1880 Discovery of the Plasmodium malarise by Laveran. 



1890 Discovery of its human developmental cycle by 

 Golgi. 



1895 Discovery of the mosquito cycle and mode of trans- 

 mission by Ross. 



iSgS : Discovery of the sexual fertilization of the parasite 

 by MacCallum. 



The interest aroused by Laveran's original discovery gave 

 a great impetus to the study of hematology with special refer- 

 ence to parasites, and it soon became evident that the plas- 

 modium was but one of a group of similar parasites. Of 

 these we have now become acquainted with the following: 



Parasite. Disease. Host. Insect host. 



Plasmodium Quartan fever. Man. Anopheles, My- 



malariae. zorrhynchus, 



Myzomyia. 



Plasmodium Tertian fever. Man. Anopheles, My- 



vivax. zorrhynchus, 



Myzomyia. 



*"Jour. of Exper. Med.," 1898, in, 117. 



