418 THE QUESTION OF IMMUNITY AND ANTITOXINS 



From these figures it will be seen : 



(a) That under five years of age 18 cases of small-pox occurred in children who 

 had been vaccinated, whilst 711 cases occurred in children who had not been 

 vaccinated. (6) That under ten years of age the cases of small-pox in vaccinated 

 persons had a mortality percentage of 1*72, and the unvaccinated cases had a 

 mortality percentage of over 42 per cent, (c) That under twenty years of age the 

 cases of small-pox occurring in vaccinated persons had a mortality percentage of 1 -93, 

 and the unvaccinated cases had a mortality percentage of 31 -27. (d) That over 

 twenty years of age the cases of small-pox occurring in vaccinated persons numbered 

 5648, and there were 680 deaths, giving a mortality percentage of 12*04 ; whereas the 

 cases occurring in unvaccinated persons were 384, 160 of whom died, giving a 

 mortality percentageof 41 -66. The larger number of cases of small-pox in vaccinated 

 persons is, of course, due to the fact that by far the larger proportion of the popula- 

 tion at that age-period have, at some time or other in their lives, been vaccinated. 

 Three broad facts stand out with clearness : (1) That small-pox among the 

 vaccinated is nowadays mainly a disease of adults, because children are protected 

 by primary vaccination and adults are not protected by re vaccination. (Ninety-two 

 percent, of the vaccinated cases were over fifteen years of age.) (2) That among 

 the unvaccinated, small-pox is still, in great measure, a disease of the young as it was in 

 prevaccination days. (Seventy-three per cent, of the unvaccinated cases were under 

 fifteen years of age.) (3) That the mortality rate among the vaccinated is at all 



