376 



SCIENCE. 



[N. S. Vol. XXIII. No. 584. 



quito during the first three days of the 

 fever, and not thereafter; the mosquito 

 being infectious after the twelfth day from 

 the date of inoculation, and not before. 

 Its victim shows the first symptom of dis- 

 ease usually in less than five days after 

 infection by the insect. 



The exceptions to this rule are not suffi- 

 cient to suggest its modification, but in 

 actual practise the patient is considered 

 possibly infectious during four days, and 

 the mosquito possibly dangerous on the 

 tenth day. 



A case of yellow fever can not occasion 

 another case in less time than the period 

 of incubation in the mosquito, which is 

 twelve days, added to the period of incu- 

 bation in its human victim, which is not 

 less than three ; fifteen days completing the 

 minimum cycle of infection. We may say 

 approximately that explosions of infection 

 should be expected, and are observable 

 semi-monthly, and the result of disinfection 

 can not be determined earlier than fifteen 

 days thereafter. We can not say how 

 many cases may result in about two weeks 

 from one case untreated sanitarily, but 

 we can say positively that no case will 

 result if there are no mosquitoes present of 

 the Stegomyia variety. Conversely we 

 may apprehend a great infection in the 

 presence of great numbers of mosquitoes. 



The application of the mosquito doctrine 

 to the prevention of yellow fever is all 

 that need be done in any emergency, but 

 to accomplish this is a problem not to be 

 solved by any set formula. It is an easy 

 matter to set down on paper and in an 

 office a lot of rules in the abstract to be 

 carried out in the field, but it is a different 

 matter to apply these rules concretely to 

 actual cases to obtain results. 



Circumstances and conditions met with 

 in actual practise may radically change the 

 relative value of details, esteemed of para- 

 mount importance theoretically. 



As applicable to a locality or community, 

 I wish to place before you three proposi- 

 tions, upon the first two of which is based 

 the third, which is offered in the nature of 

 a conclusion. 



1. Quarantine against yellow fever can 

 not be made absolute in its protective value. 



2. Early recognition of the presence of 

 yellow-fever infection is difficult always, 

 and at times impossible. 



3. The most dependable measure of pre- 

 vention of yellow fever is destruction of 

 the Stegomyia fasciata before the possi- 

 bility of infection. 



Extensive argument is not necessary in 

 an assembly of this kind whose every mem- 

 ber is qualified to do his own thinking and 

 form his own conclusions upon the evidence 

 presented. 



Quarantine. — In quarantine against yel- 

 low fever two essentials are to be consid- 

 ered, and nothing else. Detention of per- 

 sons exposed to infection for not less than 

 the period of incubation of the disease, 

 and the prevention of entrance of infected 

 mosquitoes. 



The increasing rapidity and facility of 

 travel makes quarantine more difficult and 

 less reliable. However near to perfection 

 may be our own maritime quarantine sys- 

 tem, we shall always be exposed to infection 

 by rapid land transportation from ports 

 not themselves infectible, or which are less 

 careful for other reasons. Quarantine, 

 though important and necessary, can not 

 ever be all-sufficient. 



Early Eecognition.— 'Early recognition of 

 yellow fever, so essential to the prompt 

 application of sanitary remedial measures, 

 is rarely to be expected. The history in 

 this respect of 1897-8 and 1899, as well 

 as that of 1905, exemplifies this, not only 

 in New Orleans, but elsewhere, even in 

 Havana, where better preparation is made 

 and better opportunities offer for the 

 prompt discovery of early cases. 



