648 MALARIA. 



the febrile paroxysms by a blood pamsite which invades the cells and 

 grows at the expense of the continued haemoglobin, it ma}' bo thought 

 that the etiological role of the parasite should be conceded. But scien- 

 tific conservatism demands more than this, and the final proof has been 

 afforded b}" the experiments of Gerhardt and of Marchiaf ava and Celli — 

 since confirmed by many others. This proof consists in the experi- 

 mental inoculation of healthy individuals with blood containing the 

 parasite and the development of a typical attack of periodic fever as a 

 result of such inoculation. Marchiafava and Bignami, in their elal)- 

 orate article upon "Malaria,"' published in the "Twentieth Centuiy 

 Practice of Medicine," say: 



The transmi.ssion of the disease occurs equally whether the hlood is taken during 

 the apyretie period or during a febrile paroxysm, whether it contains young para- 

 sites or those in process of development, or whether it contains sporulation forms. 

 Only the crescent forms, when injected alone, do not transmit the infection, as has 

 been demonstrated by Bastianelli, Bignami, and Thayer, and as can be readily under- 

 stood when we remendier the biological significance of these forms. 



In order that the disea.se l)e reproduced in the inoculated subject, it is not neces- 

 sary to inject the malarial blood into a vein of the recipient, as has been done in 

 most of the experiments; a sul)cutaneous injection is all-suthcient. Nor is it neces- 

 sary to inject several cubic centimeters as was done especially in the earlier experi- 

 ments; a fraction of a cubic centimeter will suffice and even less than one drop, as 

 Bignami has shown. 



After the inoculation of a health}' individual with blood containing 

 the parasite a period varying from four to twenty-one days elapses be- 

 fore the occurrence of a febrile paroxysm. Th is is the so-called period of 

 incubation, during which, nodoubt, the parasite is undergoing nuiltipli- 

 cation in the blood of the inoculated individual. The duration of this 

 period depends to some extent upon the (luantity of blood used for the 

 inoculation and its richness in parasites. It also depends upon the par- 

 ticular variety of the parasite present, for it has been ascertained that 

 there are at least three distinct varieties of the malarial parasite — one 

 which produces the quartan type of fever, in which there is a paroxysm 

 every third day and in which, in experimental inoculations made, the 

 period of incubation has varied from eleven to eighteen days; in the ter- 

 tian type, or second day fever, the period of incubation noted has been 

 from nine to twelve days; and in the testivo-autunmal type the duration 

 has usually not exceeded five days. The parasite associated with each 

 of these types of fever may be recognized by an expert, and there is no 

 longer any doubt that the difference in type is due to the fact that dif- 

 ferent varieties or "species'" of the malarial parasite exist, each having 

 a different period of development. Blood drawn during a febrile 

 paroxysm shows the parasite in its different stages of intra-corpuscular 

 development. The final result of this development is a segmenting 

 body, having pigment granules at its center, which occupies the greater 

 part of the interior of the red corpuscle. The number of segments into 



