Immunization of Rabbits. 



191 



phoids A and B, for the single strain typhoid vaccine then being 

 issued. Similar experience with paratyphoid in the British 

 Army in Flanders in the same year had also resulted there in the 

 adoption of a combined vaccine. 



This immediately brought up the question as to the basis for 

 the use of combined vaccines for prophylactic inoculation and led 

 to the initiation, in the winter of 191 7, of the experiments here 

 presented. Other workers in this field had preceded us. Castel- 

 lani 1 in 1903, showed that on injecting an animal with two different 

 organisms at the same time, agglutinins were produced for both, 

 and that the amount of agglutinin for each of the two organisms 

 was about the same as in those animals inoculated with but one 

 type of organism only. Subsequently he stated that as many 

 as six different types of bacteria might be combined in a single 

 vaccine with this same result, but that if more than six types were 

 combined, a diminished amount of agglutinin for each type resulted. 

 The problem has been attacked by other investigators, who have 

 followed the methods of Castellani, by comparing the agglutinin 

 formation when single and combined vaccines were employed. 

 As we have long known that agglutinin formation is not a real 

 index of the degree of immunity, it has seemed desirable that fur- 

 ther study of the problem should be made, in observing the 

 relative amounts of bacteriolysins produced. 



Four series of from four to five rabbits each, were immunized; 

 one series was immunized with combined triple vaccine of typhoid 

 and paratyphoid bacilli A and B; three other series with single 

 strain vaccines, — one series each with typhoid, paratyphoid A, and 

 paratyphoid B. At the beginning and end of the experimental 

 period, the blood serum of each rabbit was tested for specific 

 and group bacteriolysins and also for agglutinins. In the series 

 immunized with the single strain typhoid vaccine, all the animals 

 show a sharp rise in immunity, but an interesting paradox is to be 

 observed in the excessive production of the (group) para A lysin 

 beyond the specific typhoid lysin (the highest lytic dilution for 

 para A being 1-700,000, for typhoid 1-75,000; and for para B 

 1-400.) In the series immunized with para A vaccine, the highest 

 lytic dilution for the homologous strain is 1-20,000; for typhoid it 



1 Castellani, A., Zeitschrift f. Hyg., 1902, 40, p. 1. 



