VI 



such a horse with 500 antitoxin units pr. cc., on which 

 we inject 100 cc. of diphtheria toxin with Lt = 0,2 cc. 

 As these 0,2 cc. in vitro are neutralised by 1 antitoxin 

 unit the 100 cc. toxin injected would in vitro be com- 

 pletely neutralised by 1 cc. of the serum in question. 

 Although this horse contains 50000 times this quantity 

 of antitoxin, yet it shows a very marked antitoxin curve, 

 commencing with a rapid fall, followed by a rise to 

 1000 units pr. cc. 



The case is evidently the same as regards the agglu- 

 tinins. 



We might ask if the faculty to react with an "agglu- 

 tinin curve" is not characteristic for the actively im- 

 munised organism. That this is not the case appears 

 from the fact above mentioned, that quite fresh animals, 

 never before treated, will give the typical curve after 

 the first injection of culture. 



But perhaps an actively immunised organism might 

 have acquired a special strong affinity to the concerned 

 microbes and thus got power to break the combination 

 between the latter and the agglutinin circulating in the 

 blood. This view cannot be maintained as will be seen 

 from following experiments. 



When an actively immunised animal is injected with 

 agglutinin, a culture will not produce any agglutinin 

 curve before so long a time has passed, that most of 

 the agglutinin introduced has disappeared (curve Nr. 11.) 



This is demonstrated by a rabbit, which from the 

 13 / 2 had been actively immunised against B. typhosus. 

 On the 2fi /3, 14 days after the last injection of culture, 

 the agglutinating power of the serum was 222. An in- 

 jection of 10 cc. strong typhoid agglutinin from rabbit 

 was undertaken, which increased the liter to 833. On 

 the following day it was 588, and the animal then got 



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