MALARIAL INDEX 287 



determining the number of inhabitants showing malarial parasites in 

 the blood. This index is best determined from children between two 

 and ten years of age, as children under two show too high a proportion 

 of parasites in the peripheral blood while those over ten years of age 

 show too great an incidence of enlarged spleens. 



As before stated there are three species of malarial parasites: i. Plasmodium 

 vivax, that of benign tertian cycle, forty-eight hours; 2. Plasmodium malaria, that 

 of quartan cycle, seventy-two hours; and 3. Plasmodium f aid par um, that of aestivo- 

 autumnal or malignant tertian cycle of forty-eight hours. 



Multiple Infections. Variations in cycles may be produced by infected mosquitoes 

 biting on successive nights,J|p that one crop will mature and sporulate twenty-four 

 hours before the second. Tr^is would give a quotidian type of fever. In aestivo- 

 autumnal infections anticipation and retardation in the sporulation cause a very 

 protracted paroxysm, lasting eighteen to thirty-six hours; this tends to give a con- 

 tinued or remittent fever instead of the characteristic intermittent type. 



Plasmodium Vivax. In fresh, unstained preparations, taken at the time of the 

 paroxysm or shortly afterward, the benign tertian schizont, or nonsexual parasite, 

 is seen as a grayish white, round or oval body, whose outlines cannot be distinctly 

 differentiated from the infected red cell. They are about one-fifth of the diameter 

 of the red cell and are best picked up by noting their amoeboid activity. In about 

 eighteen hours fine pigment particles appear and make them more distinct. After 

 twenty-four hours the lively motion of the pigment and the projection of pseudopod- 

 like processes, in a pale and swollen red cell, makes their recognition very easy. 

 When about thirty to thirty ix hours old the amoeboid movement ceases. 

 Approaching the merocyte stage the pigment tends to clump into one or two pigment 

 masses and one can recognize small, oval, highly refractile bodies within the sporulat- 

 ing parasite. 



The gametes or sexual forms do not show amoeboid movement, but the fully 

 developed gamete, which is generally larger than the red cells, has abundant pig- 

 ment, which is actively motile in the male gamete and nonmotile in the female. 

 The male gamete is more refractile, is rarely larger than a red cell and shows yellow 

 brown, short rod-like particles of pigment. Abou^f teen minutes after the making 

 of a fresh preparation these male gametes "throw out four to eight long, slender, 

 lashing processes, which are about 15 to 20 microns long. These spermatozoon-like 

 bodies now break off from the useless parent cell and with a serpent-like motion glide 

 away in search of a female gamete, knocking the red cells about in their passage 

 through the blood plasma. 



The female gamete is larger than a red cell, is rather granular and has more abi 

 dant dark brown pigment than the male. 



Stained Smears. In dried smears, stained by some Romanowsky method, as that 

 of Wright, Leishman or Giemsa, we note small oval blue rings, about one-fifth of the 

 diameter of the infected yellowish-pink erythrocyte. One side of the ring is dis 

 tinctly broader than the rather fine opposite end, which seems to hold a round, 

 yellowish-brown dot, the chromatin dot, and has a resemblance to a signet ring. 

 These small tertian rings of the nonsexual parasites (schizont) are seen about the 



