56 



Table 1. — Period of incubation in yellow fever, etc. — Continued. 

 [Francis and Beyer.] 



A study of the 40 cases in this table discloses the fact that yellow 

 fever usually begins about three days after the mosquito bites. 



The period of incubation resulting from this natural method of 

 conveying the disease is rarely under three days. We have but one 

 such authentic instance, namely, two davs twenty-four hours (case 

 No. 24). 



The longest period observed was seven days five hours, but it must 

 be noted that the man who had this unusually long period of 

 incubation had previously been treated with injections of immunizing 

 sera, which may have delayed the onset and modified the disease, 

 for he had a mild attack. 



Leaving this case (No. 39) out of consideration, the longest period 

 of incubation resulting from the bites of mosquitoes is the case (No. 

 14) of Eeed. Carroll, Argamonte, and Lazear, in which an incubation 

 period of six days two hours was observed. This corresponds strik- 

 ingly to Carter's clinical observations in which he reports a case with 

 an incubation period of five and three-fourths days. See case No. 12 

 in Table 1. 



The French, commission, working in Eio de Janeiro, came to the 

 concluson that the period of incubation of the disease may be much 

 longer than this ; but we find on analyzing their work that they drew 

 their inferences largely from the disease produced by such artificial 

 means as the inoculation of modified blood serum. 



One of the conclusions of this commission was that yellow fever 

 may not infrequently incubate for twelve days before symptoms 

 declare themselves. 



They state that " this incubation of twelve days is not absolutely 

 rare. We have had occasion to see that the natural infection may 

 also present an incubation equally 16ng." 



With this statement we must take issue, for the long experience 

 of the Public Health and Marine-Hospital Service in the many 

 wars it has waged against yellow fever has amply demonstrated 

 that for practical purposes five days is sufficient to cover the period 

 of incubation of the great majority of cases. An analvsis of all the 

 cases reported in Table 1 supports this view. 



The French Commission reports several cases in support of their 

 contention. One, a young man 18 years old, who took vellow fever 

 ten days after having arrived in Petropolis from Kio"de Janeiro 

 Petropohs is a village free from yellow fever. Another instance 



