892 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



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 parasite finally 

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

 Plasmodium malarias about eight merozoites. The adult sexual forms of 

 Plasmodium falciparum are shaped like a crescent, and for that reason it is described 

 by some as the type of a genus Laverania, under the name of Laverania malaria. 

 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 chills and fever. The 

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

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

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

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

 an attack of ague on every fourth day and the disease produced 

 is called quartan fever. Patients infected by Plasmodium falci- 

 parum often have a quotidian fever with a daily rise in the temp- 

 erature, although a three day period may be recognized in some 

 cases. There are three stages in the paroxysm: during the chill, the 

 patient feels cold; in the hot stage he feels warm his temperature is 

 above normal during both stages; in the sweating stage the temperature 

 falls to normal and the patient's discomfort becomes much less. 



The regularly recurring chills and fever constitute the only symp- 

 toms characteristic of malaria and a regular rise in temperature on the 

 third or fourth days of an illness is strongly suggestive of a malarial 

 infection. The type of disease and the symptoms, produced by a 

 malarial infection, may vary almost indefinitely according to the pre- 

 cise way in which the host is harmed by the infection. Consequently, 

 an enumeration of the clinical manifestations of malaria is of less 

 importance to a student than is an understanding of the way in which 

 the malarial parasites harm their host. The malarial parasites de- 

 stroy the red cells and thus cause an anaemia with the symp- 



