266 The Control of Mosquitoes 



sources of information, the authors believe that 

 the number of cases given in this table approaches 

 the true mortality more nearly if multiplied by 

 two. Basing the estimate on a case mortality rate 

 of 33% with an average population of 15,000 

 in 1886, the number of deaths given in the statis- 

 tics is corrected to the more probable number 616 

 (308X2); the cases developed during that year 

 must have exceeded 1500 or ten per cent, of the 

 entire working force. 



The year 1886 was the fifth of the French occu- 

 pancy, the year during which the work was at its 

 height, and when the number of non-immunes 

 was comparatively high. This year can be taken 

 as a fair basis for an estimate of the mortality from 

 yellow fever that would probably have had to be 

 faced by the American forces on the Canal. The 

 average force employed by the United States 

 on the Canal was 35,000 to 40,000 mostly non- 

 immune to yellow fever. With a mortality of 

 four per cent, per annum, as was the case with 

 the French force in 1886, we should have lost 

 more than 1400 men each year from yellow 

 fever alone! 



The curves on the chart show a very interesting 

 phenomenon, in the rapid rise of yellow fever with 

 the influx of non-immunes; this rise taking place 



