MALARIA 637 



persons. Inoculation experiments on all animals except 

 man have proved negative, and in the latter the inocula- 

 tion must be intravenous. 



In the various forms of malarial fever the parasites have 

 the same general characters, though there are distinct 

 differences between them, by which they can be recog- 

 nised and the type of fever differentiated. In each there 

 is an endo-corporeal cycle within the host, through which 

 the recurrent attacks are developed ; there is also an 

 extra-corporeal cycle of development outside the body of 

 the host, whereby the infection of fresh individuals 

 becomes possible. Each of these cycles needs separate 

 description. 



If the blood of a malarial patient is examined an hour 

 or two before, or at the very commencement of, the febrile 

 paroxysm, the parasite will be recognised as a pale, ill- 

 defined mass of protoplasm within the red corpuscles, of 

 which a variable proportion are infected, the size of the 

 parasite varying in the different types of fever. When 

 some hours old a variable number of blackish pigment- 

 granules of melanin make their appearance. These sub- 

 sequently coalesce into smaller groups, and the latter again 

 into one or two larger, more or less centrally disposed, 

 masses. The parasites exhibit more or less amoeboid 

 movement, and the melanin granules are frequently in a 

 state of tremor. Later on most of the parasites (now 

 schizonts) become divided into a variable number of 

 segments which separate and become spherical, the 

 blood-corpuscle breaks down, the spherical bodies or spores 

 are set free, and a certain number of them, again becoming 

 attached to red corpuscles, develop into the first stage of 

 the parasite. The melanin granules and some of the 

 spores are ingested by phagocytes, and after some time 

 the melanin is deposited in the spleen and liver. 



The parasite, termed a plasmodium, or better, an amce- 



