BACTERIAL VACCINES 187 



teur's work, successful vaccines 1 were prepared 

 against chicken cholera and swine plague. 



The discovery of diphtheria antitoxin in 1893 by 

 v. Behring marked the beginning of the search for 

 specific sera, and it was not long before a number 

 of such were produced and employed clinically. 

 The use of sera for therapeutic purposes was very 

 attractive, because it was possible to have some 

 animal, like the horse, manufacture the antibodies, 

 and one needed then merely to transfer the animal's 

 immunity to the patient by injecting some of the 

 animal's serum. Clinical trials, however, soon 

 showed that most of these sera had little thera- 

 peutic value, and subsequently laboratory experi- 

 ments disclosed a large number of difficulties in 

 their practical application. After what has been 

 said under hasmolysins and bacteriolysins it will 

 be unnecessary to dwell on these difficulties. Among 

 them is the problem of providing sufficient com- 

 plement, the determination of the optimum dose 

 so as to avoid the parodoxical results knowp. as 

 the Neisser-Wechsberg phenomenon, the ability 

 of producing really effective antibodies, and finally 

 the question whether immunity in a given case is 

 really directly due to the presence of these anti- 

 bodies in the serum. 



1 The French have long used the term "vaccin" to denote 

 any virus which is used for immunization, and that is the 

 sense in which the term is used here. There is, of course, 

 nothing of the cow, vacca, about them. 



