54 



We have collected from the literature all the cases in which the 

 period of incubation may be stated with precision. These are of 

 course for the most part experimental cases in which the exact time 

 of the mosquito bite is known, and in which the onset of the disease 

 has been carefully observed. 



The disease usually begins sharply with a chill, pains, and rise of 

 temperature. In such cases the precise hour of onset may be stated, 

 but sometimes the attack begins vaguely or at night. Then the period 

 of incubation can be stated only approximately. In the followuig 

 table the onset of the disease is considered from the time the temper- 

 ature rises, thus omitting the prodromal symptoms of lassitude, 

 headache, etc, which sometimes send a patient to bed twenty-four 

 hours before the fever sets in. 



Of course from a practical standpoint in public health work only 

 those cases infected in a " natural " way — that is, by the bites of 

 mosquitoes, can be considered. • Subjoined is a table of 40 such cases. 



Table 1. — Period of incubation in yellow fever, resulting from bites of infected 



mosquitoes. 



[Carter: "The period of incubation of yellow fever," Med. Bee., Mar. 9, 1901; also, private cor- 

 respondence. Observations of the disease following one short exposure in the infected region 

 at Orwood, Miss., during the epidemic of 1898.] 



In these observations, which were of a clinical nature, no attempt 

 was made to determine the period of incubation within hours, any- 

 thing less than one-fourth of a day being disregarded. 



[Beed, Carroll, Agramonte, and Lazear: " The etiology of yellow fever; a preliminary note," 

 Phila. Med. Journ., Oct. 27, 1900.] 



