423 



The greater precision with which experiments of that kind can be 

 conducted upon plants than upon animals adds much value to these facts, 

 as an illustration of the extinction of a parasite by the suppression of one 

 of the two hosts required for its complete evolution. I had logically 

 inferred that the same result would have been obtained by suppressing the 

 other host instead — that is, by ceasing to plant the corn during a period 

 of time corresponding to the vitality of the spores which are produced by 

 the parasite after its growth upon the Epine vinette, on the approach of 

 summer. It was, indeed, my firm belief that the yellow fever germ could 

 only thrive within the human body until the fifth or sixth day of the 

 disease, while upon the mouth-parts of the mosquito it was able to grow 

 and multiply, with increased virulence, during several days and even 

 weeks, in fact until the death of the insect. I had not reached the more 

 advanced views concerning the development of the germ in the salivary 

 glands of the infected mosquito. By the same train of thought I was led to 

 the conclusion that yellow fever could be stamped out from an infected 

 locality either by suppressing the Culiex mosquito (Stegomyia) or by 

 preventing the approach of non-immunes to the said locality until the last 

 of the infected insects had died. In accordance with this conviction I had 

 frequently declared to my skeptical friends that if Cuba could only be 

 maintained free from yellow fever during a period of three consecutive 

 months, the infection would have to be imported anew from outside before 

 another case of yellow fever could occur. I had, however, underrated the 

 longevity of the Stegomyia, reckoning it at from thirty to forty days, 

 while we now know that some of them live as many as seventy or even 

 more days. 



I expressed my ideas on these points in a paper which I contributed 

 to the World's Congress Auxiliary of Chicago in 1893, "On Etiological 

 Factors Concerned in the Propagation of Yellow Fever;" and also in 

 another paper which I wrote for the Eighth International Congress of 

 Hygiene and Demography held at Budapest in 1894 (see Comptes Rendus 

 of the latter, vol ii, p. 702), the conclusion of which was as follows: 



' ' The special measures which might be adopted against the propagation 

 of yellow fever through mosquitoes must be left to the criterion of those 

 who accept my theory, but the principal indications must be : 



"1. To prevent those insects from stinging yellow fever patients. 



"2. To destroy, as far as possible, the mosquitoes which have been 

 infected, bearing in mind that in close spaces a temperature of 50° C. is 

 sufficient for that purpose. 



"3. Finally, to consider any place unsafe so long as the last 

 mosquitoes which have stung yellow fever patients may be alive in it ; from 

 thirty-five to forty days being the term of their existence under the most 

 favorable circumstances. ' ' 



