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considerable time (10—14 days). The same author states that 

 the medium suffers from the disadvantage that Pfeiffer's ba- 

 cillus quickly dies out on it. For its keeping qualities he 

 therefore preferred agar containing haemolysed and slightly 

 alkaline pigeon blood. Whether the inhibition of growth, which 

 unfortunately does not include the bacteria that we should 

 most expect to overgrow Pfeiffer's bacillus, is really of use, 

 is indeed rather doubtful. It must be looked at in the light 

 of Mc Intosh's previous observation that Pfeiffer's bacillus 

 from post mortem material is nearly always overgrown by 

 other bacteria on ordinary blood agar. 



The media applied by me did not possess this growth- 

 inhibiting property; according to my experience however this 

 was no disadvantage. On haemoglobin agar where the growth 

 of other organisms is favoured somewhat, and on Fildes agar 

 where they did not grow very differently than on ordinary 

 agar, Pfeiffer's bacillus has always had an easy task in asser- 

 ting itself above the other bacteria. In many cases the latter 

 have increased the growth of Pfeiffer's bacillus by their sym- 

 biotic affect on less successful haemoglobin-agar, and on media 

 containing ascitic fluid which was employed in the last ino- 

 inoculations from healthy persons. 



9. There does not seem therefore to be any reason for pre- 

 ferring the media in which an attempt has been made to i n h i- 

 b i t the other bacteria by adding special substances 

 (Avery: sodium oleate; Fleming: brilliant green; Bernstein & 

 Loewe: gentian violet). Of these, Avery's medium has been 

 largely employed. That this and the other selective media 

 can be used is undeniable, but they undoubtedly require a 

 particularly careful preparation since the inhibiting bodies can 

 hardly be entirely without action on Pfeiffer's bacillus. On 

 Avery's medium Pritchett & Stillman did not usually obtain 

 a growth of Pfeiffer's bacillus at pH. > 7.5. This slight tole- 

 rance of variations in the reaction is undoubtedly to be re- 

 garded as a sign that the conditions of growth are far from 

 optimal. The same authors did not always obtain large colonies 

 on this medium; they varied from 1 „pinpoint colonies to large 

 round colonies of 1—3 mm. in diameter". Furthermore the 

 various strains of Pfeiffer's bacillus, according to my inve- 

 stigations, are by no means all in possession of the same 



