TYPHOID FEVER 187 



The Duration of the Protection. The duration of the protection 

 all'orded by the vaccination Wright estimates at from two to three 

 years, while Xuhn 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 

 individuals who have been more or less exposed to infection, with 

 that occurring in a similar body of men, who have not been pro- 

 tected, 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 never- 

 theless 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 South West 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 enjo3 r ed 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. 



No. of No. of 



men. Morbidity. Mortality. men. Morbidity. Mortality. 



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



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



Garrison of Ladysmith 10,529 1489 329 1705 35 8 



(1899 to 1900) . . (14.14%) (3.12%) (2.05%) (0.47%) 



Army in Egypt and 2669 68 10 720 1 1 



Cyprus .... (2.55%) (0.37%) (0.14%) (0.14%) 



Hospital at Bloemfon- 178 24 53 3 



tain (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 cencentration 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 

 probable typhoid (2693 in all), with 248 deaths. Translated into 



