TYPHOID FEVER 189 



TYPHOID FEVER 



After Pasteur had shown that it is possible to produce active 

 immunity in animals against such diseases as chicken cholera, 

 anthrax, and swine plague, the thought naturally suggested itself 

 that the same should be possible in the case of some of the organisms 

 which are pathogenic for man. Attempts in this direction showed, 

 as a matter of fact, that it is perfectly feasible to protect the common 

 laboratory animals against infections like typhoid and cholera, and 

 that this end can be reached not only by the use of living cultures, 

 but even with the killed organisms. The latter discovery is, of 

 course, of the greatest importance, as it unquestionably hastened 

 the application of the findings in the animal experiment to the 

 prophylactic treatment of the human being. The great question 

 naturally has been how large a dose of bacilli should be injected and 

 how frequently the injections should be made in order to secure 

 adequate protection. Pfeiffer and Kolle, who were probably the 

 first to attempt this in the human being, thought that the bacterioly- 

 tic content of the serum might possibly be used as an indicator in 

 this respect, while Wright, to whom we are indebted for the actual 

 introduction of the method into common use, once thought that 

 the opsonic content of the blood might prove of service in this respect. 

 Subsequent studies, however, have shown that a parallel between the 

 size of the dose, the serum content of protective substances, and 

 the degree of immunity does not exist, and we may say that our 

 present methods are essentially the outcome of actual trial, irre- 

 spective of any special index. 



Preparation of the Vaccine. Wright recommends that the culture 

 from which the vaccine is to be made should first be brought to a 

 certain degree of virulence by animal passage, and that its rate of 

 growth in twenty-four hours should yield from 1000 to 2000 million 

 bacilli per c.c. of bouillon. The first point can be reached by passing 

 the organism through a few guinea-pigs, while the second has to be 

 tried out. Whether either condition is really imperative may be 

 questioned. To my mind it is more important that the vaccine 

 should be polyvalent, i. e., that it should represent a mixture of 

 a number of different strains. As medium for growth ordinary 

 1 per cent, peptone broth is used, which should be as nearly neutral 



