194 ACTIVE IMMUNIZATION 



The Duration of the Protection. The duration of the protection 

 afforded by the vaccination Wright estimates at from two to three 

 years, while Kuhn speaks of a single year. 



Results. In the human being it is, of course, out of the question 

 to study the protective value of the vaccination, as is possible in 

 the animal experiment. All that we can do is to compare the rate 

 of morbidity from typhoid fever in a large body of vaccinated indi- 

 viduals who have been more or less exposed to infection, with that 

 occurring in a similar body of men who have not been protected, 

 and who have been exposed to a similar extent. We can further 

 compare the rate of mortality among the non-vaccinated with that 

 of those who have been vaccinated, but who have nevertheless 

 developed the disease. Studies of this kind have been carried on 

 in the English army at the time of the Boer War, in the German 

 army in Southwest Africa, and lately in the United States concen- 

 tration camp on the Mexican border (1911). 



Some of the data obtained in the English army are given in the 

 accompanying table, from which it is clear that the vaccinated 

 individual enjoyed a much greater security, both as regards the 

 probability of infection, and the outcome, in the event that the 

 disease nevertheless developed: 



Non-vaccinated. Vaccinated. 



Men. Morbidity. Mortality. Men. Morbidity. Mortality t 



Indian Army (1899) . . 25,851 657 146 4502 44 9 



(2.54%) (0.56%) (0.89%) (0.2 %) 

 Garrison of Ladysmith 



(1899 to 1900) . . 10,529 1489 329 1705 35 8 



(14.14%) (3.12%) (2.05%) (0.47%) 

 Army in Egypt and 



Cyprus .... 2,669 68 10 720 1 1 



(2.55%) (0.37%) (0.14%) (0.14%) 

 Hospital at Bloemfon- 



tain 178 24 53 3 



(14%) (5.6 %) 



From this table it is also clear that the protection is not absolute. 



The results obtained in our own army are even more striking. 

 It will be recalled that both the morbidity and mortality from 

 typhoid fever in our concentration camps at the time of the Spanish 

 war were perfectly appalling. In a body of 10,759 men there were 

 thus 1729 cases of certain typhoid, and in addition 964 cases of 



