OTHEK PROTOZOA 89 



recognized by the intervals between successive chills, (i) Ter- 

 tian fever, caused by Plasmodium vivax, is characterized by an 

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

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

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

 falciparum, produces attacks daily or more or less constant fever. 

 The life histories of these three species of Plasmodium differ 

 very slightly one from another. Plasmodium vivax has been 

 selected for presentation here as a type of the group Sporozoa. 

 The various stages that occur during the life cycle of this parasite 

 offer a mass of detail that can only be adequately discussed in a 

 larger work, so we shall simply give a brief outline of the chief 

 phases. 



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 prevent 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. Constant 

 reference to Figure 42 will make the following description 

 clear. 



At the time of their entrance the parasites are slender boat- 

 shaped cells pointed at both ends, and are called sporozoites 

 (XIX). These sporozoites immediately penetrate the red blood 

 corpuscles by means of wriggling movements. Inside of the 

 blood corpuscle the sporozoite becomes ameboid in shape, and 

 begins to feed on the surrounding protoplasm (I). As it grows 

 larger a vacuole develops, giving it a ringlike appearance (II and 

 III). When fully grown the parasite almost completely fills the 

 blood corpuscle and its ameboid movements cease (IV, V, and 6). 

 Within its body can be seen a number of dark br,own granules 



