122 TROPICAL MEDICINE AND HYGIENE 



Though the cause has not been discovered, it is now 

 known, as the result of the experimental work of Reed 

 and Caroll, fully confirmed by numerous observers, that 

 the infective agent is imbibed with the blood of patients 

 by certain mosquitoes, and that such mosquitoes, after 

 a definite period of ten to twelve days, are in turn capable 

 of infecting non-immunes. These experiments have 

 shown : 



(1) That neither in the vomit, black or otherwise, in the 

 faeces, or sweat, or other discharges from the patients is 

 any infective agent contained, but that it is contained in 

 the blood during the first three days of the attack. 



(2) That mosquitoes (Stegoniyia fasciata) can convey 

 the disease, and that the other common and domestic 

 mosquitoes do not so carry the disease. 



The condition necessary for the conveyance of the 

 disease by these mosquitoes are : 



(a) That the mosquito must have fed on the blood 

 of a yellow fever patient during the early stage, first, 

 second or third day of the disease. 



(b) That the mosquito must have lived for ten days 

 or more after this feeding. 



(c) That the person bitten in the second instance must 

 be susceptible. 



This series of events shows that the parasite of yellow 

 fever requires development in the mosquito before it 

 can be injected into man, and that it is not simply a 

 transference of the organisms from one man to another. 



Marchoux and Simond claim that the mosquitoes may 

 transmit the organism to their offspring, though the more 

 extensive observations of Rosenau and Goldberger have 

 failed to confirm these results, and the method in which 

 yellow fever is spread is in more accordance with the 

 transmission by the adults than in this manner. 



The period of incubation of yellow fever after the bite 

 of an infective mosquito varies little and is usually from 

 three to four days, very rarely over five. In persons 

 partially immune a longer period of incubation may be 



