APPLICATION OF THE PHENOMENON 397 



87 to 88 reacting units oi the homologous filtrates. This tact was 

 considered instructive, for this high degree of immunity appeared 

 iniexpectedly after persistent innnunization with the active prin- 

 ciples and the meningococcus ctiltures for a period of forty-one 

 ^veeks. 



It was also noted in this work that horses ^vhich were imder 

 ordinary treatment for as long as one year and which were then 

 in addition ptit on stibcutaneous treatment with active filtrates 

 did not respond readily with the development of neutralizing 

 antibodies. Normal horses ^vhich ^vere immunized from the very 

 beginning by both std)cutaneotis injections of active principles 

 and intravenotis injections of live meningococctis cidtines, in less 

 than t^vo months gave sera capable of consistent neutralization of 

 40 reacting miits of Group I filtrate. 



Interesting information could be obtained when ^veekly trial 

 bleedings were tested for the neutralizing antibodies over a pro- 

 longed period of time. In one horse stich tests Avere done dining 

 the period of immunization from the eighth until the fifteenth 

 month. During this period there were observed pronounced fluc- 

 tuations in the concentration of nentralizing antibodies. The anti- 

 bodies appeared suddenly at the eighth month and reached a 

 high level ^vithin the two following ^veeks {i.e., over 100 Group 

 I neutralizing units) . This rise was followed by a fall in titer in 

 spite of continued immunization. Then again, there w^as a sud- 

 den rise in titer. It was also significant that the high titer which 

 appeared six days after the last injection came do^vn two days 

 later. Inasmuch as there were observed drops in titer in spite of 

 continued immtuiization, it ^vas thought advisable to determine 

 whether a rest ^vould not reestablish the ability of the horses to 

 produce antibodies. After thirty-eight days of rest one horse re- 

 ceived a small dose of toxic filtrate, subcutaneously and a mixture 

 of filtrate with serum, intravenously. This single injection stimu- 

 lated production of antibodies of high titer which also remained 

 at the same level after the second injection but came down after 

 the third injection and stayed \o^v for a number of the following 

 weeks of treatment. 



In another example, also instructive, the neutralizing anti- 

 bodies appeared shortly after beginning of the immunization. 

 Thus, fifteen days after the second injection the serum neutralized 

 completely 25 units of Group III reacting factors and twenty- 

 two days later, it neutralized completely 50 units of Group I 



