Protective vaccinations 483 



might up to a certain point serve as the measure of the immunity 

 acquired against typhoid fever. His own researches, however, showed 

 him that this supposition could not be maintained, and that the 

 agglutinative power, varying greatly in strength, might sometimes be 

 absent where the immunity could not be denied. On the other hand, 

 he clearly showed, especially by the experiments with serum collected 

 at the period which precedes the relapses, that the agglutinative 

 property might be highly developed, in spite of the absence of im- 

 munity. Wright then set himself to study the bactericidal property 

 of the serum of individuals who had been injected with his vaccine. [506] 

 He devised a very ingenious method of gaining with a minimum loss 

 of time some idea of the fluctuations of this power of the body fluids 

 to kill the typhoid coccobacillus. In the first place he demonstrated 

 that the bactericidal property is not at all parallel to the agglutinative 

 power, and this has further confirmed him in his opinion that there 

 may be no direct relation between it and acquired immunity. He has 

 found further that the power of the blood serum to destroy the 

 typhoid coccobacillus is very variable in persons vaccinated by his 

 method. After injections of large quantities of these killed bacilli 

 this power may even be diminished for a very long period. On the 

 other hand, medium or small doses of the vaccine first set up a 

 negative stage, during which the bactericidal property is very feeble, 

 and later they bring about an increase of this property, often very 

 marked. Wright does not think that the bactericidal power can 

 serve as the measure of the immunity acquired by the vaccinated 

 individuals, but he hopes that some day a method may be found 

 suitable for the examination of the blood which will give us informa- 

 tion as to the degree of immunity conferred by the antityphoid 

 vaccination. For the present the only basis upon which we can form 

 any opinion on this subject is furnished by statistics. Now we know 

 that it is often very difficult to collect data that are sufficiently exact 

 Hence during the war in South Africa, where one-fifth of the English 

 troops, that is to say about 50,000 persons, were submitted to 

 vaccinations by Wright's method, it is only in certain cases that the 

 statistical information can be utilised. Many of the patients attacked 

 by slight fevers are omitted from the statistics, because from the 

 absence of a precise diagnosis it is not known whether they should 

 come under the category of typhoid patients or not. In other cases 

 the secondary complications divert the attention of the doctors and 

 prevent the registration of a proper diagnosis. 



31-2 



