THE SPOROZOA 247 



dinn's detailed monograph [94a] of the tertian parasite contains nothing 

 to support Billet's view. 



The schizogony is most easy to study in the two species of Plasmodium, 

 since in them it commonly takes place in the peripheral circulation, and 

 rosette - stages can be obtained in a drop of blood from the finger or 

 elsewhere. In Laverania, on the other hand, the sporulation goes on, 

 as a rule, in the internal organs, and its stages are difficult to obtain. 

 The multiplication of the nuclei in the schizont commences by a primitive 

 form of mitosis, but as the nuclei increase in number, the method of 

 division becomes a simpler type of multiple nuclear fission (Schaudinn 

 [94a]). The schizonts are distinguished by trifling differences of pigment- 

 ation in the three species, and also by variations in the process of 

 sporulation. In the quartan parasite the rosettes have a form which has 

 been compared to that of a daisy, and are relatively few, from nine to 

 twelve in number. In the tertian species the merozoites are more 

 numerous, usually from twelve to twenty -four in number, and the 

 corresponding stage has more the form of a mulberry. In Laverania the 

 forms of the rosettes, and the number of the merozoites in each, are very 

 variable. Most characteristic, however, is the length of time required 

 by each species to complete a generative cycle. In P. malanae a 

 schizogonous generation, from sporozoite (or inerozoite) to merozoite, 

 occupies seventy-two hours ; in P. vivax, forty-eight ; while in Laverania 

 it is twenty-four hours or of irregular duration. 



By repeated schizogony the numbers of the parasites in the 

 blood increase by geometrical progression, in a way similar to the 

 Coccidia in an infected epithelium, until a very large number of 

 the corpuscles are infected and destroyed. Apparently the only 

 check to the multiplication of the parasite is to be found in the 

 activity of the leucocytes, which sometimes capture and destroy 

 a merozoite or other free stage. It is evident that reproduction 

 at this rate could only continue indefinitely in the ichor of an 

 infinite host. In the blood of an ordinary mortal of limited 

 capacities the results are most dangerous and even fatal. 

 Provision is therefore soon made for the transference of the 

 parasite to fresh hosts and new spheres of activity by the 

 development of certain merozoites into sexually differentiated 

 schizonts or gametocytes, the appearance of which is the 

 prelude, as in Coccidia, to reproduction by sporogony. In Laver- 

 ania the gametocytes are distinguished at once from ordinary 

 schizonts by their peculiar form, like that of a sausage, slightly 

 bowed, and considerably exceeding in length the diameter of the 

 blood-corpuscle, the remains of which are seen in the concavity of 

 the gametocyte (Fig. 68, Vila, VIK). Hence these forms of the 

 parasite, very characteristic of pernicious malaria, are commonly 

 known as " crescents." The gametocytes are not all alike, how- 

 ever, but can be separated into two categories, distinguished, 

 though not always very sharply, by the arrangement of the 



