VACCINATION AGAINST TYPHOID 387 



serum not only the primary typhoid agglutinins but also such 

 secondary agglutinins as those acting on the b. coli. If, how- 

 ever, an animal had undergone infection with, say, both the 

 b. typhosus and the b. coli, then the b. typhosus could not absorb 

 from its serum the b. coli (primary) agglutinin. Castellani thus 

 put forward the view that by this means primary could be 

 differentiated from secondary agglutinins, and therefore pure 

 could be differentiated from mixed infections. There is little 

 doubt that this view possesses considerable validity, though it is 

 probably not of universal applicability. Safe deductions can 

 only be drawn when any serum is tested with several species of 

 fairly closely related organisms, such as those of the coli group. 

 Especially is it necessary that the highest dilutions in which 

 agglutination occurs should be compared. If such precautions 

 be adopted, the absorption method can be utilised for the differ- 

 entiation of the typhoid and paratyphoid organisms and their 

 infections, and for similar investigations. 



Vaccination against Typhoid. The principles of the im- 

 munisations of animals against typhoid bacilli have been applied 

 by Wright and Semple to man for prophylactic purposes. The 

 method of preparing the vaccine has been described on p. 135. 

 Two doses are usually given separated by an interval of ten 

 days. The first consists of 500,000,000 bacilli and the second 

 of 1,000,000,000. The effects of the first injection are some 

 tenderness locally and in the adjacent lymphatic glands, and 

 it may be local swelling, all of which come on in a few hours, 

 and may be accompanied by a general feeling of restlessness 

 and a rise of temperature, but the illness is over in twenty-four 

 hours. During the next ten days the blood of the individual 

 begins to manifest, when tested, an agglutination reaction, and 

 further, Wright has found that usually after the injection there 

 is a marked increase in the capacity of the blood serum to kill 

 the typhoid bacillus in vitro. The second injection usually 

 produces practically no symptoms, but ought to be followed by 

 a further rise in agglutinins in the serum. These observations, 

 there is little doubt, indicate that the vaccinated person possesses 

 a degree of immunity against the bacillus, a conclusion borne 

 out by the results obtained in the use of the vaccine as a 

 prophylactic against typhoid fever. Extensive observations 

 have been made in the British army in India, and in the South 

 African War the efficacy of the treatment was put to test. 

 Though in isolated cases not much difference was observed 

 among those treated as compared with those untreated, yet the 

 broad general result may be said to leave little doubt that on the 



