Yellow Fever and Other Diseases 105 



because: (i) It is absolutely necessary for its continued 

 existence that it pass alternately through man and the 

 mosquito, and the parasitic existence in those hosts is ob- 

 ligatory. (2) The fact that a period of about two weeks 

 or more must elapse before the contaminated mosquito is 

 capable of infecting, points to a definite cycle of develop- 

 ment in that insect. (3) The limitation of its develop- 

 mental cycle to mosquitoes of a single genus, and to a 

 single vertebrate, conforms to a natural zoological law, 

 and does not agree with our present knowledge of the 

 life history of bacteria. (4) The effects of climate and 

 temperature upon Stegotnyia, and upon the rate of de- 

 velopment of the yellow-fever parasite within the body of 

 that insect, are exactly the same as the effects of the same 

 conditions upon the Anopheles mosquito and the malarial 

 parasite." 



Infection. — The shortest period of incubation 

 within the insect is twelve days. The invalid usu- 

 ally manifests the first symptoms within five days 

 after having been bitten, and the germ is accessible 

 to new mosquitoes only during the first three days 

 of the fever. To be on the safe side, however, the 

 physicians hold the patient as possibly infectious for 

 four days, and the mosquito so on the tenth. The 

 shortest term in which the disease can be transmitted 

 from one patient to another is the sum of the two 

 periods of incubation, that of the insect and of the 

 human — fifteen days in all. 



Yet, in spite of all the experiments of Reed, 

 Carroll, Lazear and Agramonte in Cuba (described 

 at length in Dr. Howard's Mosquitoes and in other 

 publications), which clearly demonstrated that sup- 



