PHYLUM PROTOZOA 51 



parallel to the surface on which it alights, whereas the abdomen 

 of Anopheles is held at an angle. 



There are three well known types of malaria; these may be 

 recognized by the intervals between successive chills, (i) 

 Tertian fever, caused by Plasmodium vivax, is characterized by 

 an attack every forty-eight hours; (2) quartan fever, caused by 

 Plasmodium malaria, with an attack every seventy-two hours, 

 and (3) estiw-autumnal or pernicious fever, caused by Plas- 

 modium falciparum, produces attacks daily, or more or less con- 

 stant fever. The life histories of these three species of Plas- 

 modium differ very slightly one from another. 



Tertian fever is transmitted by diseased female mosquitoes 

 only. The mouth parts of these insects are adapted for piercing. 

 When they have been thrust into the skin of the victim, a little 

 saliva is forced into the wound. This saliva contains a weak 

 poison, which is supposed to prev int the coagulation of the blood 

 and thus the clogging of the puncture. Blood is sucked up by 

 the mouth parts into the alimentary canal of the mosquito; 

 this process occupies from two to three and a half minutes. 

 With the saliva a number of parasites, which were stored in the 

 salivary glands of the insect, find their way into the wound. 

 The human blood corpuscles are immediately entered by the 

 parasites, and their contents slowly consumed. Finally the 

 blood corpuscle breaks down, and the spores, which were formed 

 within it by the parasite, escape. 



The malaria parasite multiplies very rapidly, and the " chill " 

 so characteristic of the disease results either from the simul- 

 taneous destruction of great numbers of blood corpuscles or 

 from the liberation of a poison produced by the parasites. 

 When a mosquito bites a malaria patient, it sucks up some 

 of the parasites with the blood. These parasites pass through 

 part of their life history within the alimentary canal and 

 body cavities of the insect, and, after a period of multiplica- 

 tion, make their way into the salivary glands. They are then 

 ready to be injected into the next human being the mosquito 



