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 following 
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. Rec., 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.] 
Case No.— 
Bitten. 
Attack. 
Ihcubation. 
1 
3 days. 
Do. 
Between 3 and 4 days. 
Do. 
Do. 
Do. 
Do. 
Do. 
4 days. 
Do. 
4| days. 
5f days. 
2 
3 
4 __ 
5_ 
6_ 
7 
8.. 
9 
10 
11... 
12...... 
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. 
[Reed, Carroll, Agramonte, and Lazear: “ The etiology of yellow fever; a preliminary note,” 
. Phila. Med. Journ., Oct. 27, 1900.] 
Case No.— 
Bitten. 
Attack. 
Incubation. 
13 (10). 
Aug. 27, 2 p. m_ 
Aug. 31 (?) a. m.. 
3 days 17-22 hours (about). 
14 (11).- 
Aug. 31, 11 a. m_ 
Sept. 6 (?) p. m_ 
6 days (about). According to the 
authors, 6 days 2 hours. 
