83^ MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



bodies and become a macrogamete and the microgametocyte produces severa:! micro- 

 gametes, one of which enters and fertilizes the macrogamete. Through the fusion of 

 macrogamete and microgamete a copula is formed, which since it is motile is called an 

 o8kiuet. This makes its way until it comes to lie just beneath the outer surface of 

 the mosquito's stomach. There it develops, as an oocyst, until it reaches several 

 times its original size. It divides into a number of areas, or sporoblasts, each of 

 which subdivides to form many very small, hair-like sporozoites. When the oocyst 

 bursts, some of the sporozoites pass forward to find their way into the salivary 

 glands of the mosquito, and, when it bites, they are extruded, with the saliva, into the 

 body of the person from whom blood is being sucked. The entry of a sporozoite 

 into a red cell recommences the cycle of development which has just been 

 described. If the adult sexual parasites are not taken up by a mosquito they die 

 off in the blood, but some of the female forms may live for years and then divide 

 parthenogenetically, without a precedent fertilization, to produce several young 

 parasites. It has been suggested but never demonstrated that the sporozoites 

 may enter eggs lying in the ovaries of infected mosquitoes and that mosquitoes, 

 hatched from such eggs, may inherit the infectioA from. their parent and that 

 they, also, are able to transmit malaria. 



In fresh preparations of blood, a malarial parasite is seen as a body of varying 

 size, which is more refractile and of a lighter color, than the red cell which contains 

 it. In its growing phase it has distinct amoeboid movement and the pigment 

 granules lying in it are in active motion. In preparations, stained by a modification 

 of Romanowsky's method, every malarial parasite is seen to possess a definite purple 

 nucleus surrounded by blue-staining cytoplasm. Young parasites measure less 

 than a fifth of the diameter of a red cell in width; adult parasites may completely 

 fill the cell which contains them. Malarial pigment is the waste product which 

 results from the digestion of the haemoglobin of the red cells by a malarial parasite, 

 and consequently, since they have digested more haemoglobin, the older parasites 

 contain more pigment than do the younger ones. A mature asexual finally 

 segments into a nuinber of merozoites; Plasmodium vivax forms about eighteen, 

 Plasmodium malaria about eight merozoites. The adult sexual forms of 

 Plasmodium falciparum are shaped like a crescent. The three malarial parasites 

 of man may be distinguished from one another by these peculiarities as well as by 

 other, lesser differences in themselves and in the red cells which they parasitize. 



When a mature, asexual, malarial parasite bursts, it sets free young 

 parasites and a toxin. Practically all of the parasites, present in a 

 person suffering from typical acute malaria, mature and burst at the 

 same time and the considerable amount of toxin, set free in this way, 

 produces a paroxysm characterized by chiUs and fever. The 

 parasites of Plasmodium vivax mature in forty-eight hours. Conse- 

 quently, a person infected by it has a chiU when schizogony occurs, 

 on every third day, and the disease caused by it is called a tertian 

 fever. Plasmodium malarim matures in seventy-two hours, causes 



