57 



was a girl 12 years old, who was taken with yellow fever ten days 

 after returning from Eio, her father having sent her to Petropolis 

 because his wife and three other children had the fever. 



We do hot doubt that Petropolis is " indemne," free of Stegomyia 

 fasciata, and that the disease has never been known to spread there; 

 but the communication with Eio 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 case 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 yellow 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.] 



No. 1 received subcutaneously 2 cc. Hood 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. blooi taken on second day. 



No. 4 received subcutaneously 1 cc. blood taken 27± hours after commencement of disease. 



[Heed and Carroll; " The etiology of yellow fever; a supplemental note," Am. Med., Feb. 22, 1902.] 



Case 5 received subcutaneously 0.75 cc. partially defibrinated blood 15J hours old. 



