CHAPTER VII 



YELLOW FEVER AND OTHER DISEASES 



Is Yellow Fever a Protozoan Disease? — Al- 

 though the parasite of yellow fever has never been 

 found, the chances are that, like malaria, it is a proto- 

 zoan. There are striking resemblances between the 

 two diseases. Both occur in low areas and are com- 

 monest in the situations where, and seasons when, 

 mosquitoes are most abundant, disappearing after the 

 severe frosts, which drive the insects into hibernation. 

 Direct inoculation of the blood of a patient will 

 convey either disease. To quote from Dr. Calkins's 

 paper, read at the meeting of the American Associa- 

 tion for the Advancement of Science in New 

 Orleans : — 



" The asexual protozoan organisms are transferred from 

 the warm blood of birds, or mammals, or man, to the cold 

 environment of the insects' digestive tract. This is ac- 

 complished in the case of malaria by mosquitoes belong- 

 ing to the genus Anopheles ; in the case of bird malaria, 

 by Culex ; in the case of sleeping sickness, by the tsetse 

 fly; in the case of Texas fever among cattle, by ticks 

 belonging to the genus Boophilus. Where the full life 

 history has been made out, it has been found that con- 

 jugation takes place within the body of the insect, and 

 here, therefore, vitality of the parasite is restored. What 



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