IMMUNISATION OF ANIMALS. 337 



peculiar to the toxins of the B. typhosus. As to the nature 

 of the typhoid toxins, we know nothing. Martin has, however, 

 found that in the case of the typhoid bacillus there is very little 

 digestive action, such as occurs with the bacilli of diphtheria and 

 tetanus. 



The Immunisation of Animals against the Typhoid Bacillus. — 

 In considering this question we must note : ( i ) immunisation 

 against the living bacilli; (2) immunisation against their tox- 

 ins ; and (3) the relations between these two conditions. Earlier 

 observers had been successful in accustoming mice to the typhoid 

 bacillus by the successive injections of small and gradually 

 increasing doses of living cultures of the bacillus. Later, Brieger, 

 Kitasato, and Wassermann found that a bouillon made from an 

 extract of the thymus gland contained bodies which were inimical 

 to the virulence of the typhoid bacillus, though the medium was 

 sufficiently nutritive to permit of their multiplication. A culture 

 three days old in such a bouillon, killed by heating at 60° C. 

 for fifteen minutes, and injected into mice, was without fatal 

 effect. Ten days later it was found that these mice could 

 tolerate an otherwise fatal dose of the original living virulent 

 culture. The experiments were repeated on guinea-pigs with 

 a similar result, and it was also found that the serum of a 

 guinea-pig thus immunised could, if transferred to another 

 guinea-pig, protect the latter from the subsequent injection of 

 a dose of typhoid bacilli to which it would naturally succumb. 

 Chantemesse and Widal, SanarelU, and also Pfeiffer, succeeded 

 in immunising guinea-pigs against the subsequent intraperito- 

 neal injection of virulent living typhoid bacilli, by repeated and 

 gradually increasing intraperitoneal or subcutaneous doses of 

 typhoid cultures in bouillon, in which the bacilli had been killed 

 by heat or chloroform vapour. Experiments performed with 

 serum derived from typhoid patients and convalescents indicate 

 that similar effects occur in those who have successfully resisted 

 the natural disease. Thus many observers had noticed that the 

 serum of men convalescent from typhoid had an inimical effect 

 on typhoid bacilli. Pfeiffer found that the serum of healthy men 

 might have such an action but in a much less degree. The 

 method was to mix the serum and the bacilli in a little bouillon, 

 and inject the whole intraperitoneally into guinea-pigs. He 

 found that when the latter did not die, the bacilli became 



