107 



complete absence of growth on ordinary peptone 

 broth agar as a characteristic of Pfeiffer's bacillus, but we 

 must be more cautious in our interpretation of growth on 

 ascitic agar. It would obviously lead to absurd results to 

 exclude all bacteria that occasionally can be made to grow on 

 one or other batch of ascitic agar, from the species „Pfeiffer's 

 bacillus". The boundary between growth and absence of growtli 

 on ascitic agar is much too indistinct and what is more, it is 

 far too susceptible to slight variations in the constitution of 

 the medium. As will appear from what follows, quite diffe- 

 rent results may be obtained with the same strains when 

 the medium 1 is prepared in different ways even though the 

 same agar and ascitic fluid are used each time. Still greater 

 variations will be encountered by employing different ascitic 

 fluids. It must be remembered that such fluids, quite apart 

 from the blood content, can vary considerably in constitution 

 and in their value as nutritive media for bacteria. Nor is it 

 excluded that that amount of haemoglobin which is too small 

 to give the benzidin reaction, may be useful to Pfeiffer's ba- 

 cillus. Ascitic fluid seems to inhibit this blood reaction to 

 some extent so that a greater concentration of haemoglobin 

 is required for a positive result than in a watery solution 

 or a solution in broth. (Nevertheless most of the ascitic fluids 

 I investigated reacted strongly with benzidin, without being 

 perceptibly redlinted). 



Although ascitic agar does not lend itself to purely routine 

 work in the same way as ordinary agar, it would be improper 

 not to include it among the means which serve to distinguish 

 Pfeiffer's bacillus, because the fact that an organism grows 

 excellently on agar containing dissolved „haemoglobin", in con- 

 junction with the fact that on carefully prepared ascitic agar 

 it grows at most, only scantily, is very characteristic of Pfeif- 

 fer's bacillus and some closely allied species. When the test 

 on ascitic agar is carried out with all the four requirements 

 mentioned above, fulfilled, the interpretation of the result will 

 certainly not involve any difficulty. 



. It was mentioned that some strains of Pfeiffer's bacillus 

 which had been cultivated for over I1/2 years, behaved exactly 

 like recently isolated strains as regards growth on a slightly 

 blood-containing ascitic agar. This indicates that the nutritive 



