195 



On 13. IV. 21 strain „l 37" was tested against the same sera 



I 6 40. 40. 100. 100. 100. 100. 100. 100. 100. 



I 57 0. 0. 20. 60. 100. 100. 100. 100. 100. 



I 91 0. 0. 0. 20. 40. 100. 100. 100. 100. 



I 21 0. 10. 20. 40. 60. 100. 100. 100. 100. 



I 33 10. 20. 60. 100. 100. 100. 100. 100. 100. 



I 34 0. 0. 0. 0. 20. 40. 100. 100. 100. 



I 35 10. 20. 40. 60. 80. 100. 100. 100. 100. 



I 37 0. 0. 0. 0. 0. 0. 0. 0. 10. 



Me la 0. 0. 0. 40. 100. lOO.'lOO. 100. 100. 



Pa 5 0. 0. 0. 0. 10. 20. 60. 80. 100- 

 Two normal 



rwo normal \ 



rabbit sera / in each case 10a 



In both the experiments all the sera were tested in the first 

 three quantities without the addition of the culture. There was 

 no inhibition in any of the cases. 



It will be seen that complement fixation, at any rate with 

 the technique employed, brings out a more extensive rela- 

 tionship between the various strains of Pfeiffer's bacillus than 

 agglutination did; but the lack of homogeneity of the material 

 makes itself felt to a very marked degree here also. 



For instance, serum I 6 reacts very strongly with its homologous 

 strain but practically not at all with strain I 37, and strain I 6 

 reacts considerably more vigorously with sera I 21 and Pa 5 than 

 with serum I 37, while the converse holds in the case of strain I 37. 



We can therefore conclude, with the knowledge of the 

 experiments brought forward, with lolerable certainty that the 

 present material cannot be collected under one heading by com- 

 plement fixation tests with monovalent rabbit serum 1 . Further- 

 more, not only these but also the other complement fixation 

 tests decisively indicate that there are even gradations from 

 strong heterologous reactions to entirely absent reactions, so 

 that no natural classification within the Pfeiffer's bacillus group 

 can be undertanken. 



Summary of the Characters of Pfeiffer's Bacillus. 



We have investigated a collection of bacterial strains which 

 were defined by the rules given on pp. 99 — 100, all the strains 



13* 



