TYPHOID FEVER 195 



cated a more energetic procedure. This would suggest itself as 

 especially advisable in the treatment of individuals in whom a longer 

 interval has elapsed between the bite of the rabid animal and the 

 beginning of treatment. Hogzes thus begins with virus fixe, using 

 high dilutions at first (1 to 10,000), from which he gradually ascends to 

 strong ones (1 to 100), and Ferrori even starts with full virulent virus 

 fixe in large doses and reports favorable results. 



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 in 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 a human being, thought that the bacterio- 

 lytic 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 



