

VARIETIES OF THE MALARIAL PARASITE. 481 



set free on the death of the insect, thus gaining access to 

 water. But regarding this, definite evidence is still required. 



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 differ- 

 ences 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 agree- 

 ment 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 crescent ic bodies do not occur. 

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

 spring " fevers of Italian writers) were first distinguished by 

 Golgi. Their characters are the following : 



1. Quartan. The parasite passes through its cycle of 

 development in twelve hours, and all the various stages are 

 found in the blood. Only the smaller forms within the red 

 corpuscles show amoeboid movements, and these are not 

 of very active character. The red corpuscles invaded by 

 the parasite do not become decolorised or altered in 

 size ; the pigment granules are somewhat coarse. Typical 

 rosette-forms are seen in the process of sporulation, which 

 results in the formation of six to twelve segments or spores. 

 The spores in the fresh blood show a central clear spot 

 which is not seen in the spores of the tertian parasite. 



2. Tertian. The cycle of development of the parasite 

 is completed in forty-eight hours. The young forms within 

 the red corpuscles show much more active movement than 

 in the quartan type, and give off longer and more slender 

 processes, whilst the pigment granules are finer. The 

 infected corpuscles become swollen and pale. Sporulation, 



