404 



every insect, specially those which feed on human Blood, must be provided 

 by nature with buccal secretions which are germicidal for the generality 

 of germs which may occur in the blood of the sick, Ijest some of them 

 should prove fatal to the insect itself and annihilate the species. This may 

 perhaps be one of the functions of the venom glands. In that case the power 

 of transmitting yellow fever, as exhibited by the Stegomyia, should not be 

 considered as an additional] functional manifestation on the part of this 

 insect, but on the contrary as a deficiency in the germicidal power of its 

 venom as compared with that which is displayed by the venom of other 

 blood sucking insects. The yellow fever germ will thus pass unharmed into 

 the stomach of the Stegomyia and continue therein the mosquito phase of 

 its existence, while in the case of any other blood-sucking insect it would 

 have been destroyed or inhibited by the venom. So long as the true germ 

 of yellow fever remains unknown, this hypothesis cannot be directly verified 

 under the microscope; but the principle seems to be confirmed in the case 

 of the malaria parasite, which passes unscathed through the buccal cavity 

 of the Anopheles and continues to develop in the stomach of its host, while 

 in the other species of gnats it reaches the stomach already doomed to 

 degeneration and death. 



Having thus presented what I consider to be a plausible explanation 

 of the fact that only certain kinds of blood sucking insects are capable of 

 transmitting certain germs, and that some species of the same family of 

 insects may exhibit that peculiarity while the other species do not, I have 

 only to add that so far, no valid reason has been brought forward for 

 supposing that any other insect but the mosquito is capable of transmitting 

 yellow fever, nor even that any other species of mosquito but the Stegomyia 

 fasciata is capable of doing so. 



