disease have failed," whereas all successful attempts have been with 

 such mosquitoes as had been allowed to feed on cases during the first 



three days. 



There are some who, while granting that the mosquito is capable of 

 transmitting the disease directly by biting, maintain that the disease 

 may also be acquired by ingesting water in which the body of an 

 infected mosquito has disintegrated. Again, there are others who, 

 while admitting that the mosquito is the sole medium of transmission, 

 hold, nevertheless, that there may be sources other than the one men- 

 tioned from which this insect may acquire its infection, and suggest 

 black vomit or articles soiled by yellow-fever patients as pertinent illus- 

 trations. But neither the results of experiments especially designed 

 to test these hypotheses nor the indirect evidence furnished by a large 

 mass of observations give the slightest support to these assumptions. 

 After the mosquito has become infective it probably remains so for 

 life. 



B. — Tdlow fever can be produced under artificial conditions by the 

 subcutaneous injection 'of blood taken from the general circulation 

 ofapers«n sick with this' disease during the first 3 days of his illness. 



The subcutaneous injection of a drop* (0.1 cc.) of yellow fever blood 

 serum from a case in the first day of illness has produced an attack of 

 yellow fever, whereas five times this amount from a case in the fourth 

 day of the disease produced no symptoms. 



C. — Yellow fever is not conveyed by fomites. 



Before the demonstration by the Army Commission of the trans- 

 mission of yellow fever through the mosquito it was very generally 

 believed, notwithstanding a large mass of evidence to the contrary, 

 that the disease was communicated by the exhalations of. the sick, by 

 contact with their excretions, or with articles that had been exposed 

 to or been soiled by them. 



In order to put this almost universal belief in fomites to a rigorous 

 test, the Army Commission exposed each of a series of seven non- 

 immunes to clothing and bedding which had been used by cases of 

 yellow fever and which had become soiled with blood, urine, feces, 

 and black vomit. The house in which the experiment was carried 

 out was especially constructed for the purpose in an isolated place 

 near Habana. In order to prevent access of mosquitos and to siniu- 



«The recorded experimental evidence is not sufficient to show that this infective 

 period may.not at times extend into the fourth day. This is of considerable prac- 

 tical importance. A case of yellow fever should be protected from mosquitoes during 

 four full days at least. 



6 Parker, Beyer, and Pothier (1903) induced an attack of yellow fever by the sub- 

 cutaneous injection of 0.033 cc. of filtered serum from a case in the third day. 



