EXPERIMENTS IN TRANSMISSION 249 



inoculation of the existing mosquitoes. Finally, the importance of the experi- 

 ments from the point of view of prophylaxis can not be disregarded." 



This case is so extremely important that more space must be devoted to it. 

 The year following the first announcement just quoted, fuller details were given 

 in the Annals of the Pasteur Institute for January, 1906, in which the symptoms 

 of the infected patient are carefully given, day by day, and the daily tempera- 

 ture is charted, leaving the case fairly open to the inspection and possible criti- 

 cism of yellow-fever experts. The investigators consider a light attack of 

 yellow fever as perfectly proved, and state that the absence of albumen, the 

 lowering of the temperature after forty-eight hours, and the rapidity of the 

 convalescence particularly show the mildness of the case. They consider that the 

 immunity to a subsequent attack, which they tested by later inoculations with 

 infected mosquitoes, is also strong evidence of the validity of the first attack, 

 and in fact confirms it rigorously. They call especial attention also to the fact 

 that the interval between the time of the first infective bite, 4 o'clock in the after- 

 noon on the 10th of March, and the appearance of the first symptoms of yellow 

 fever at midday on the 14th of March, being three days and twenty hours, or 

 ninety-two hours, is exactly the interval most commonly observed in experi- 

 ments in the transmission of yellow fever by the bite of Aedes calopus. They 

 point out that in the twenty-six experimental cases followed by positive results 

 at Havana and in Brazil eighteen cases showed symptoms of the fever in the 

 course of the fourth day following the bite. 



They considered the possibility whether, in spite of their careful watch over 

 the subject, who as a matter of fact lived with one of them in the laboratory, 

 some chance circumstance had perhaps exposed him to inoculation other than 

 the experimental puncture of the hereditarily infected mosquito. But they 

 think that there was no chance that this could have occurred under the precise 

 conditions. 



In the article just cited the French writers admit that it is impossible to draw 

 ■unassailable conclusions from an isolated case. However they elaborate upon 

 the importance of this discovery as accounting for the return of recently stamped- 

 out epidemics at a period which may be comparatively short but too long to 

 permit of its direct carriage by adult mosquitoes infected before the epidemic 

 was stamped out. They cite the return of the 1889 epidemic at Campinas as a 

 possible example. Eeverting again to the benignity of the case produced by the 

 hereditarily infected mosquito, they ask if this was not due to an attenuation 

 of the virus which had passed through the egg and larval stages of the insect. 

 They state that among their experimental cases bitten by directly infected mos- 

 quitoes they found a certain proportion which were benign, and concluded that, 

 aside from individual resistance to the disease, there are conditions as yet un- 

 known which bring about an increase or an attenuation of the virus in the mos- 

 quito. They argued further that it is known that in countries where yellow 

 fever occasionally exists there are false epidemics — an illness known under the 

 name of inflammatory fever. It differs from yellow fever by the mildness of its 

 attack and by the absence of mortalities. One of these writers studied in 1882 a 



