152 



of oxygen is plainly seen on cultivation in haemoglobin broth. 

 Rapid and prolific growth takes place principally when the tubes 

 are laid obliquely, — almost horizontally, so that the medium 

 has a large surface exposed to the air. In such a tube 

 Pfeiffer's bacillus develops chiefly at the upper end where 

 the layer of fluid is quite thin. 



In March 1920 all the cultures named on p. 108 were inocu- 

 lated on haemoglobin agar in Petri plates which as usual were 

 placed upside down. In the cover a small flat dish was pat in 

 which the solutions of pyrogallol and alkali were poured in such 

 a way that as far as possible they did hot become mixed. The 

 space between the bottom and the cover was sealed with paraffin 

 and plasticine, after which by gently rocking the plate the liquids 

 in the interior dish were made to mix. In this way a large ab- 

 sorbing surface in relation to the air space is obtained. Under 

 these conditions none of the strains grew. 



The experiment was repeated in December 1920 with all the strains 

 which were alive at that time (see p. 110 (1. XI. 1921)), among which 

 there were also strains from guinea-pigs. I 103, I 32, 33, 36, 37; 

 Ms 1, 13, 15; Me la; H 49b, 127, 156, 157, 159, 261-288, 318—327, 

 344, 346 and 352 grew poorly (much worse than in the presence of 

 air), while the other strains did not grow at all. Presumably the 

 anaerobic conditions were not so complete as in the previous ex- 

 periment. The spinal strains were tested separately and did not give 

 any, or only very slight growth. 



It must therefore be said that on the whole the strains 

 examined behave similarly as regards the need of oxygen. It 

 would be of interest to get a clear idea of the causes of the 

 divergent experiences of different authors on the relation of 

 Pfeiffer's bacillus to oxygen. 



Relation to the Reaction of the Medium. 



In July 1919 ordinary haemoglobin agar of 4 different reactions 

 was prepared. By colorimetric determination (indicators: neutral red, 

 rosolic acid, and phenolphthalein) the p^. value was found to be, 

 6.5, 6.8, 7.4, and 8.6 in the different samples. Each of the 4 media 

 was inoculated with the strains I 6, I 74, I 21, and II 31. The 

 growth on the first 3 plates was good and about the same in 

 each case; on the last it was scanty. Although the determinations 

 are not very accurate it can be stated that Pfeiffer's bacillus is 

 not particularly sensitive to variations in the reaction of the medium- 



