464 VETERINARY BACTERIOLOGY 



of the corpuscle is filled. When full grown, it may double the 

 diameter of a blood-cell. The organism then segments to form a 

 rosette of bodies, which round off to form small spores or merozoites. 

 These are freed by the disintegration of the red blood-cell, and 

 attach themselves to other cells and begin development anew. This 

 may be repeated several times. This is called the asexual phase 

 of the life-history. The organism may be taken in by the mos- 

 quito (Anopheles), and here completes its life-cycle by passing 

 through the sexual phase. Two types of cells are found to de- 

 velop from the spores in the body of the mosquito. The male 

 cell (known as microgametocyte) produces five to eight micro- 

 gametes. The female cells (macrogametes) are larger and granu- 

 Jar. A microgamete fuses with one of the macrogametes to form 

 what may be termed a fertilized " egg," copula, or ookinete. 

 This burrows into the wall of the stomach of the mosquito, 

 encysts, and enlarges greatly. The contents finally break up 

 into a considerable number of spherical bodies known as sporo- 

 blasts. These in turn produce great numbers of delicate fila- 

 mentous bodies called sporozoites. These are liberated by the 

 rupture of the cyst, and pass through the body cavity, and 

 finally enter the poison or salivary gland, whence they are 

 inoculated into the next victim of the mosquito. This cycle in 

 the insect is completed in from eight to ten days, and during this 

 time the insect is not infective. 



Pathogenesis. The disease is characterized by chills, followed 

 by fever, which occur every forty-eight hours. The infection is 

 usually benign; a fatal termination is very rare. The chills and 

 fever develop at the time of formation of the merozoiites and the 

 infection of new cells. 



Transmission. The disease is transmissible only through the 

 bite of the mosquito. The elimination of the possibility of this 

 transfer is the all-important factor in efficient prophylaxis. 



Plasmodium malarias 



This organism produces the quartan malaria in which the 

 interval between paroxysms of fever is seventy-two hours, and tin- 

 asexual cycle is completed in this time. This disease, like the 

 preceding, is benign, and yields readily to quinin treatment. 



