134 General Biology 



into the blood-stream where (within an hour) they may again attack and 

 enter other red blood cells. 



The breaking up of the red blood cells takes place at the moment 

 the merozoite is mature, and the chills and fever likewise appear at this 

 time. 



It will be readily understood that, when thousands of red corpuscles 

 are thus removed from the circulation, the patient will be pale 

 (anaemic). The chills may be due to the haematozoin granules, which 

 possibly contain poisonous substances. 



This process of the merozoites being thrown out of the red cor- 

 puscles into the blood stream may continue for some time, but after 

 a while, rounded forms, which throw off tiny filaments, appear. These 

 are the male sexual forms, while the larger macrogametes are the female 

 forms. Both male and female forms, however, require a mosquito as 

 host before being able to develop further. The sexual cycle, already 

 described in the mosquito's body, now begins, if the infected individual 

 is bitten by a female Anopheles mosquito. 



The chills always appear at regular intervals, because the incubation 

 period of each of the three kinds of malarial parasites (although differing 

 for each species) is always the same for the same species. Thus the 

 tertian fever species (Plasmodium vivax) "hatches" every third day — 

 hence its name ; the quartan (Plasmodium malariae) every fourth day 

 while the aestivo-autumnal type (Plasmodium immaculatum Laverania) 

 at irregular intervals. In fact, the physician uses this definite incubation 

 period as his clue in diagnosing the case, to find what particular type 

 of malarial parasite has infected his patient. . 



After the spores or merozoites are thrown into the blood-stream, 

 many are devoured by the white corpuscles (leukocytes), but those not 

 devoured, again enter new red corpuscles and so continue reinfecting 

 the same patient, although they are unable to infect another. 



The method of communication from one person to another can only 

 come about in the following manner: 



A female mosquito of the genus Anopheles must suck the blood 

 of an infected person if the disease is to be communicated. As soon 

 as the infected blood reaches the changed environment of the mosquito's 

 stomach, the series of changes begins in the merozoites, which have been 

 described above. It will thus be seen that Plasmodium malariae must 

 not only pass through two stages of a life-cycle, sexual and asexual, but 

 these two stages are unable to develop in a single host, the asexual stage 

 developing in man, and the sexual in mosquitoes. 



At this point the question will occur, "How do we know all this?" 

 It is the answer to this question which will give the student (1) the 

 finest illustration of what modern laboratory methods mean ; (2) it will 

 acquaint him with the exhaustive investigations which students of 

 science are always performing, and (3) it will show him what great 



