314 COLLECTED STUDIES IN IMMUNITY. 



method of Neisser and Wechsberg, namely, approximate estimation, 

 because only large results were regarded as conclusive. Frequently 

 after the six drops had been taken from the tube, the residue was 

 again placed into the incubator. In this way one often obtains 

 valuable confirmation of the agar plates by noting whether or not 

 there is a growth in the tubes. 



The strongest bactericidal power is possessed by goat and sheep 

 .sera, but this is but slight in comparison to their action on many 

 other species of bacteria. 0.3 cc. of these sera almost completely 

 killed the bacteria under the conditions mentioned. Other sera are 

 weaker, such as ox, horse, human, dog, guinea-pig, and rabbit serum. 

 A reactivation of normal inactive sera succeeded only in the follow- 

 ing combination: normal inactive goat serum could be completely 

 reactivated by normal active horse serum in an amount which by 

 itself did not kill the bacteria. These experiments showed that only 

 a few sera could be used for reactivation (e.g. horse serum) apparently 

 because the other sera did not contain any considerable excess of 

 free dominant complement, or contained none at all. This was 

 entirely confirmed by the complementing experiments which were 

 made with a high-grade immune serum. The immune serum used 

 was obtained from a horse which I myself had begun to immunize 

 and which had been further immunized in the meantime. The serum 

 was sent to me from Japan with the addition of 0.5% carbolic. In 

 the small amounts in which the serum was used, this addition in no 

 way disturbed the bactericidal experiments, as was shown by control 

 tests. The first experiments undertaken with the completion by 

 means of active horse serum resulted negatively in so far as any 

 destructive action was concerned. This was soon found to be due 

 to the phenomenon of complement deflection described by Neisser 

 and Wechsberg; for when smaller and still smaller doses of the immune 

 serum were employed the destructive action became more and more 

 marked. Table I, in which column A gives the result of the plate 

 tests, and B that of the test-tube experiment made at the same time, 

 shows the destructive action as well as the phenomenon of comple- 

 ment deflection. 



From this it is seen that even 0.0025 and 0.0005 cc. still have a 

 distinct bactericidal action. This result was obtained a great many 

 times, with various strains, in almost the same manner. 



Besides the horse serum only one other serum could be used 



