YELLOW FEVER 2 59 



ably spread by mosquitoes, and it has been definitely determined 

 by Carrol and Reed that the female Aedes capolus (formerly 

 called Stegomyia fasciata and St. calopus) is the means of its 

 propagation. Carrol believes that the undiscovered parasite of 

 yellow fever is of the animal kingdom, for the following reasons: 

 (i) It is absolutely necessary for its continued existence that it 

 undergoes alternate generation in man and in the Stegomyia 

 mosquito. This is peculiar to the sporozoa. (2) The fact that 

 twelve days must elapse before the mosquito is capable of infect- 

 ing man is evidence that a cycle of development of the unknown 

 parasite is taking place in the mosquito. (3) The limitation of the 

 cycle of development of the parasites to a single genus of the 

 mosquito and to a single vertebrate (man) conforms to a natural 

 zoologic law, and this does not conform to our knowledge of the 

 life history of bacteria. (4) The effects of climate and tempera- 

 ture on the life history of the Stegomyia, and on the rate of 

 development of the parasites in the bodies of the mosquitoes are 

 exactly the same as the effects of the same conditions on 

 the anopheles mosquito and the malarial parasite. Without the 

 Stegomyia there can be no yellow fever. Infection requires the 

 fulfilling of the following conditions: (i) By the bite of the mos- 

 quito providing the insect has fed on the blood of a yellow fever 

 patient within the first three days of the fever. (2) The disease 

 is not transferred immediately, but a definite incubative period 

 of more than eleven days must elapse before the mosquito can 

 transfer the disease. After twelve days the mosquito has been 

 found to be infected for at least fifty-seven days. (3) Yellow 

 fever cannot be carried by fomites. (4) Yellow fever may be 

 produced in a healthy man by the subcutaneous injection of blood 

 from a yellow fever case (parasites in the blood). (5) The serum 

 of a yellow fever patient filtered through a very fine Berkef eld or 

 porcelain filter is still capable of setting up the disease if injected, 

 proving that the infection agent is capable at some stage of its 

 life to pass through filter pores. (6) An attack of yellow fever 



