522 MALARIAL FEVER. 



completely worked out in the case of the malarial parasite. 

 If such a result is established it of course does not follow 

 that the disease is always transmitted by the bite of a 

 mosquito, as there are other means by which the extra- 

 corporeal forms of the parasite may gain entrance to the 

 human body, e.g. by drinking water, possibly by inhalation, 

 etc. 



The origin of the pigmented cells in the stomach of the 

 mosquito has not yet been traced, but light is thrown on the 

 subject by the observations of MacCallum on halteridium, 

 another protozoon infecting birds. He found that outside 

 the body some of the flagellated forms entered certain of 

 the parasites which had escaped from the corpuscles and 

 assumed a rounded form. As a result these latter, impreg- 

 nated as it were, became vermicules with powers of inde- 

 pendent movement and containing pigment in their interior. 

 A similar process probably occurs in the stomach of the 

 mosquito, the vermicules afterwards penetrating the gastric 

 wall. This confirms Hanson's view, mentioned above, that 

 the flagella are really flagellated spores. Koch regards 

 them in a similar light, calling them spermatozoa. 



Varieties of the Malarial Parasite. The view pro- 

 pounded by Laveran is that there is only one species of 

 malarial parasite, which is polymorphous, and presents 

 slight differences in structural character in the different 

 types of fever. This view is now held by only a small 

 minority of authorities, and it is generally believed that 

 there are several distinct varieties, though there is still 

 diversity of opinion as to their exact number. There is, 

 however, a fairly general agreement as to the division of 

 the varieties of malarial fever, according to the characters 

 of the parasite, into two main classes ; the first including 

 the milder forms, tertian and quartan, and the second 

 including the quotidian, malignant, and certain irregular 

 forms. The following arrangement follows closely that of 

 Marchiafava and Bignami, and of Mannaberg. 



(a) Milder forms, in which crescentic bodies do not occur. 

 The parasites of the quartan and tertian fevers (" winter- 



