57 
was a girl 12 years old, who was taken with yellow fever ten days 
after returning from Rio, her father having sent her to Petropolis 
because his wife and three other children had the fever. 
We do not doubt that Petropolis is “ indemne,” free of Stegomyia 
fas data, and that the disease has never been known to spread there; 
but the communication with Rio is close, and if yellow fever cases are 
brought to Petropolis it is conceivable that infected mosquitoes may 
also be carried. There are many other “ loopholes ” which weaken 
observations of this kind, and we have therefore refrained from 
placing them in our table. 
The last case cited by the French commission is as follows: 
On board the vessel Messageries, returning to Europe, having taken passengers 
from Rio de Janeiro, an isolated ease of yellow fever declared itself among the 
latter passengers between Dakar and Lisbonne; that is, nine to fourteen days. 
It was our experience that some cases of yellotv fever are so mild 
that they are detected with difficulty, especially under such unfavor¬ 
able conditions as on board ship. “ The isolated case ” on board the 
Messageries may have been the second case, especially as the fourteen 
days is sufficient to cover the “ extrinsic incubation ” of the disease. 
The literature has several instances of such cases. They should be 
carefully considered before drawing definite conclusions. 
It is interesting to compare the period of incubation resulting from 
exposure to infection in the “ natural” way with the period of incuba¬ 
tion resulting from experimental yellow fever, produced by the inocu¬ 
lation of blood or blood serum. The following table shows 17 such 
cases: 
Table 2. —Period of incubation in yellow fever , resulting from the injection of 
blood. 
[Reed, Carroll, and Agramonte: “Experimental yellow fever,” Am. Med., July 6,1901.] 
Case No.— 
Inoculated. 
Attack. 
Incubation. 
1 
Jan. 4, 11 a. m__ 
Jan. 8, 9 a. m. 
3 days 22 hours. 
2 days 12 hours. 
1 day 19 hours. 
3 days 1 hour. 
2 
Jan. 8, 9 a. m_ 
Jan. 11, 9 a. m.. 
3 
Jan. 22, 1 p. m.. 
Jan. 24, 9 a. m.... 
4_.__ 
Jan. 25,12.45 p. m_ 
Jan. 28, 1.15 p. m_ 
No. 1 received subcutaneously 2 cc. blood taken on second day. 
No. 2 received subcutaneously 1.5 cc. blood taken 12 hours after beginning of attack. 
No. 3 received subcutaneously 0.5 cc. bloo t taken on second day. 
No. 4 received subcutaneously 1 cc. blood taken 27f hours after commencement of disease. 
[Reed and.Carroll: “ The etiology of yellow fever; a supplemental note,” Am. Med., Feb. 22,1902.] 
Case No.— 
Inoculated. 
Attack. 
Incubation. 
5(3).... 
Oct. 15, 4 p. m_ 
Oct. 20, 6 p. m_ 
5 days 2 hours. 
Case 5 received subcutaneously 0.75 cc. partially defibrinated blood 15^ hours old. 
