660 INFECTION AND IMMUNITY. 



the disease unless they also have sucked malarial 

 blood. The conditions are different in relation 

 to Texas fever, in which the infection is trans- 

 mitted by the female tick to her young. 



The aestivo-autumnal parasite apparently is 

 more virulent than the tertian or quartan. Not 

 all cases of tertian or quartan fever are equally 

 severe, and these variations may depend on differ- 

 ences both in virulence and in the resistance of in- 

 dividuals. When all the parasites divide within a 

 period of from two to four hours, the paroxysm is 

 more intense but shorter than when division ex- 

 tends for from six to eight hours (Ruge in rela- 

 tion to tertian fever). Some of the severer symp- 

 toms are due to the localization of the parasites 

 (brain and intestines), rather than to special tox- 

 icity. 



Ratn f ^ e me l anem i a ^ malarial fevers is due to the 

 fact that the parasites absorb the hemoglobin from 

 the erythrocytes, transform it into melanin by 

 their metabolic activities and liberate the melanin 

 at the time of cell division. The anemia results 

 from destruction of the erythrocytes. 



The cause of the fever and its periodic recur- 

 rence is more difficult to explain. As stated above, 

 the fever begins in both tertian and quartan fevers 

 at the time division forms of the parasites are en- 

 countered in the peripheral blood. Although all 

 the parasites do not divide simultaneously, the 

 process is complete within a period of four to 

 eight hours and the paroxysm begins early in this 

 period. It is quite natural, then, to infer that by 

 the division of the parasite and the escape of the 

 Fever and y oun ce ^ s from the erythrocytes, toxic substances 

 are thrown into the circulation, and that the febrile 



