MALARIA. 363 



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

 tal inoculation of healthy individuals with blood containing the para- 

 site and the development of a typical attack of periodic fever as a result 

 of such inoculation. Marchiafava and Bignami, in their elaborate 

 article upon 'Malaria/ published in the 'Twentieth Century Practice of 

 Medicine/ say: 



"The transmission of the disease occurs equally whether the blood 

 is taken during the apyretic period or during a febrile paroxysm, 

 whether it contains young parasites 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 demon- 

 strated by Bastianelli, Bignami and Thayer, and as can be readily un- 

 derstood when we remember the biological significance of these forms. 



"In order that the disease be reproduced in the inoculated subject it 

 is not necessary to inject the malarial blood into a vein of the recipient, 

 as has been done in most of the experiments; a subcutaneous injection is 

 all-sufficient. Nor is it necessary to inject several cubic centimeters, as 

 was done especially in the earlier experiments; a fraction of a cubic cen- 

 timeter will suffice and even less than one drop, as Bignami has shown." 



After the inoculation of a healthy individual with blood containing 

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

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

 incubation, during which, no doubt, the parasite is undergoing multipli- 

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

 period depends to some extent upon the quantity 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 aestivo-autumnal 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 

 which this body divides differs in the different types of fever, and there 

 are other points of difference by which the several varieties may be dis- 

 tinguished one from the other, but which it is not necessary to mention 



