598 INFECTION AND IMMUNITY. 



Active im- and Baumgarten, with their followers, have prac- 

 ticed assiduously the artificial immunization of 

 animals with the tubercle bacillus or various prep- 

 arations from the organism, with the hope of pro- 

 ducing active immunity to the disease. Williams. 

 Webb and Barber have successfully immunized 

 animals by the injection of living virulent tubercle 

 bacilli into the subcutaneous tissue. In these 

 experiments, the immunization was begun with a 

 single isolated tubercle bacillus as the first dose. 

 The immunity was demonstrated by the fact that 

 the animals were able to withstand the injection of 

 many times the fatal dose of living tubercle bacilli. 

 The indications are that in preparation of tubercle 

 bacillus vaccines by heat, etc., the antigen ic prop- 

 erties of the bacilli are unfavorably modified. Eel- 

 atively avirulent strains as those cultivated from 

 fish, turtle or fowls, have been utilized for the first 

 injections. As immunization progresses one of two 

 processes may be followed : either the quantity in- 

 jected may be increased gradually, as when killed 

 or avirulent bacilli are used, or the immunization 

 having been begun with avirulent living cultures 

 those of higher virulence may be substituted later. 

 In any case immunization is difficult and slow, 

 and many animals may be lost from cachexia or 

 from tuberculosis which develops from hasty pro- 

 gression in dosage. The subcutaneous injection 

 of intact cells has the disadvantage that local ab- 

 scesses frequently develop, and to avoid this the 

 intravenous injection of smaller doses has been 

 practiced in some instances. For active immuniza- 

 tion the "new tuberculin" of Koch containing all 

 the cellular constituents in a finely divided form 

 has the advantages that it may be given subcu- 



