PATHOGENIC PROTOZOA. 419 



small, round, colorless, hyaline body within the red corpuscle, 

 seen during and just after the chill of the disease. This body 

 may be actively ameboid, suddenly changing its contour into 

 various forms. Its size gradually increases, and fine, dark, 

 actively motile, dancing pigment granules begin to appear at 

 its periphery. 



The red corpuscle harboring the parasite, with the growth 

 of the latter, becomes gradually paler and expands in size. 

 The parasite as it grows loses its earlier ameboid movement, 

 and the pigment granules, still actively motile, accumulate. 

 Near the end of forty- eight hours the organism finally fills 

 the red corpuscle, only a faint rim indicating the latter. The 

 ripe parasite now divides it into from fifteen to twenty-five 

 small, round, hyaline spores, which are arranged somewhat 

 radially about the pigment granules which have lost their 

 motility and become concentrated in a clump at the center of 

 the spore-forming organism. The spores finally break apart 

 and scatter, each destined to invade a red corpuscle and 

 start anew the cycle of development. This cycle may be 

 repeated over and over again, producing a corresponding 

 number of malarial paroxysms. 



Certain full-grown parasites do not complete the cycle of development by 

 sporulation, as described, but, breaking loose from the corpuscle, remain as 

 "extracellular" bodies. These are seen chieiiy after the paroxysm as large, 

 round, pale bodies containing numerous dancing pigment granules scattered 

 through their substance. They ultimately degenerate and disappear. Some 

 of these extracellular forms may be seen to develop long slender processes, 

 flageUa, having a very active w^hip-like motion. Flagella are never observed 

 in perfectly fresh blood, but develop only after the blood has been drawn some 

 time, usually fifteen or twenty minutes. 



The extracellular forms of the parasite, the gametes, incapable of further 

 development in their human intermediate host, can continue their life cycle 

 only when, by chance, they happen to be sucked into the body of a mosquito 

 of the genus Anopheles, the definite host, in which they undergo a second com- 

 plete sexual cycle of development with the ultimate production of spores or 

 sporozoids. When in turn the spores chance to be inoculated into the blood 

 of man by the bite of an infected Anopheles, the man becomes infected, and 

 the cycle of development in the red corpuscle, already outlined, commences. 

 The second or sexual cycle of the parasite in the mosquito, here described 

 for the tertian organism, applies as well to the other varieties of the malarial 

 organism, namely the quartan and the estivo-autumnal forms, in the case of 



