spores or the oocyst reach the intestine of another animal, in which 

 case the cyst membranes are dissolved by the digestive juices and 

 the sporozoites are set free to infect the host cells. 



The Haemosporidia are sporozoa parasitic in the blood of 

 various hosts. They are of several types, the most important being 

 that of the Plasmodium group of malaria organisms. 



Malaria as a disease is of three principal kinds, known as 

 tertian, quartan, and quotidian or aestivo-autumnal fever. The 

 organism of tertian fever is Plasmodium vivax. The fever phase 

 in malaria is periodic, occurring every 48, 72 or 24 hours (third day, 

 fourth day, daily) according to the type of infecting organism, or 

 in the quotidian kind resulting from multiple infection. Trans- 

 mission takes place through the bites of mosquitoes of the genus 

 Anopheles, ordinary mosquitoes of the genus Culex not carrying 

 the organism. 



The life history resembles that of Coccidium in most respects. 

 The two phases are as follows : 



(a) Re-infection of the host. The organism penetrates the red 

 blood cells. Multiple division or schizogony follows with produc- 

 tion of merozoites. These are set free by destruction of the host 

 corpuscle and each is able to penetrate a new cell. The formation 

 of the merozoites is coincident with the fever phase of the disease, 

 and it is in this phase that the use of quinine as a specific is effective. 



(b) Transmission stages. Macrogametes and microgametes are 

 formed, the latter being thread-like cells given off from the side of 

 the parent cell which, after the sperms are formed, becomes a 

 residual body. Fertilization takes place only in the body of the 

 mosquito host. The fertilized eggs are motile vermicules, ookinetes, 

 which penetrate the wall of the intestine, and taking a position 

 behind the epithelium give rise to large oocysts. These contain, as 

 a result of repeated division, hundreds or even thousands of pointed 

 sporozoites. They escape from the cyst and are found distributed 

 through the tissues of the mosquito host, including those of the 

 salivary glands. Salivary secretion thrown from the glands into 

 the oral tube of the mosquito is the medium by which a second 

 human host is infected. 



The association of malaria with low-lying regions is determined 

 by the breeding habits of the Anopheles host, the larvae of which 

 are aquatic. Removal of malaria infection is made possible by 

 drainage, use of kerosene, which prevents the larvae from breathing 

 the surface air on which they depend for respiration, and intro- 

 duction of small fishes which feed on the larvae. 



Febrile conditions are periodic because of uniform times of 



