158 



from a comparison between the experiments in March and No 

 vember in the case -of those strains examined at botli these times. 

 The 4 strains which gave no growth in the experiment ,,25° 1" 

 and were also examined in November at 23°, still did not grow. This 

 and several similar concurrences are probably not fortuitous. 



With regard to the minimum temperature for growth, the 

 present collection of strains of Pfeiffer's bacillus therefore form 

 a group in which it can vary over a range of about 5°, namely 

 from 20° to 25°, and, — at any rate under the present con- 

 ditions of cultivation — it must be accepted as a fairly con- 

 stant factor for each individual strain. 



As regards the position of the minimum temperature my ex- 

 periments are in accord with those of Auerbach (cited from 

 Czaplewski) and Luerssen who obtained growth at 22°. Pfeif- 

 fer's (2), Jundell's, and Davis' statements that 23°— 28° is the mi- 

 nimum temperature for growth, will therefore at best only ripply 

 to a few strains of Pfeiffer's bacillus. Presumably these divergencies 

 depend on differences in the media used, the method of inoculation etc. 

 I could not however, by inoculating different strains on Fildes 

 agar and on blood agar, and keeping them at a temperature at 

 which only a few of the strains grew, discover any indication that 

 the minimum temperature for growth on the two media was different. 



Resistance to Heating, Drying, and Keeping. 



A fact that is very often put forward as characteristic of 

 Pfeiffer's bacillus is its slight power of withstanding various 

 deleterious agencies.. Thus Onorato found it was killed by 

 heating to 45° for half an hour and drying for 1/4 — 2V2 hours, 

 according to the temperature and the degree of humidity of 

 the air. Many authors testify to the tendency of cultures of 

 Pfeiffer's bacillus to die out quickly, in that they have to be 

 subcultured at intervals of 3—6 days, if one wants to be 

 certain of keeping them alive, but this does not exclude the 

 possibility, of course, that in some cases they might continue 

 to live for 2—3 weeks. But it must be remembered that this 

 very limited resistance only refers to surface cultures and 

 even from these Davis (2) obtained growth after 3 months, 

 although only after the tubes were kept sealed. This must 

 be regarded as an exception. Deep down in suitable media 



