160 ESSENTIALS OP BACTERIOLOGY. 



of quartan fever. 3. The Hcemomenas przecox, the parasite of 

 sestivo-autumnal fever. 



According to its situation, the parasite exhibits two distinct 

 phases of existence : in the human blood it passes through an 

 asexual reproductive cycle, while in the body of the mosquito 

 it undergoes an entirely different series of sexually reproductive 

 changes. It is simpler first to describe the life history of the 

 organism in general, pointing out the differences shown by the 

 three varieties later. 



1. The Asexual Cycle in Man. An infected mosquito conveys 

 the parasites into the blood as minute hyaline bodies which 

 enter the blood-cells. At first they are small, round, colorless 

 bodies, exhibiting more or less active amoeboid motion in the 

 fresh blood. Sometimes, particularly in the a3stivo-autumnal 

 form, a ring shape is assumed. Their size gradually increases 

 and pigment granules appear, while in stained specimens a 

 nucleus containing chromatin granules is visible. As the para- 

 site approaches maturity the chromatin becomes scattered, 

 and finally the protoplasm divides into six to twenty spores 

 (merozoites), each containing a portion of the chromatin. The 

 number of spores formed and their arrangement before seg- 

 mentation takes place differ in the three varieties and will be 

 noted below. The spores burst through the envelop of the red 

 corpuscle and become free in the blood, but speedily enter fresh 

 corpuscles and pass through the same series of changes. The 

 febrile stage is synchronous with sporulatioii and liberation of 

 the young forms. 



Certain of the parasites do not, however, go on to segmenta- 

 tion, but, after reaching maturity, remain quiescent and form 

 the so-called gametes or sexual types. In the tertian and quartan 

 varieties these are not very different from the mature organ- 

 isms, but the festivo-autumnal gametes are crescentic in shape 

 and very characteristic. 



2. The Sexual Cycle in the Mosquito. If, now, the blood is shed, 

 certain of the gametes (the male forms or microgametocytes) ex- 

 trude long protoplasmic processes containing a central core of 

 chromatin, and which represent the male fertilizing element 

 (microgametex). These become detached, and, entering a female 



