230 



mass of culture, agar with heat coagulated blood is probably to 

 be preferred. 



Besides the haemoglobin agar and Fildes agar other media 

 were made use of in some cases in the large series of investi- 

 gations as mentioned on pp. 88—89. As regards the „dark red" 

 blood agar referred to, it has always happened that when the 

 blood agar was prepared in the „normal manner" by mixing 

 agar cooled to about 40° with blood previously heated to the 

 same temperature, Pfeiffer's bacillus grew in minute colonies 

 only, just visible to the naked eye. By heating the liquid 

 mixture of agar and blood to such an extent that it assumed 

 a dark red colour a medium was obtained on which Pfeiffer's 

 bacillus grew considerably better. By further heating the blood 

 agar till the colour became chocolate-brown the growth was 

 still richer. This „chocolate agar" however I have only ex 

 ceptionally used, as the transparent media with dissolved hae- 

 moglobin and pepsin-digested blood gave a sufficiently good 

 growth for my purpose. 



In some of the mass inoculations from 1 healthy persons 

 various other media besides those ordinarily used, were em- 

 ployed. Thus all the inoculations on 5. III. 19. were made 

 on the usual medium containing haemolysed horse blood and 

 also on agar containing the haemolysed blood in some cases 

 of pigeon and in others of different samples of human blood. 

 The pigeon and horse blood gave almost equally good results, 

 while all the three samples of human blood were distinctly 

 less effective. 



The medium referred to on p. 88 which was used for the 

 inoculations on 21 IX. 21. was prepared from agar to which 

 was added 25»/o ascitic fluid, dissolved haemoglobin until the 

 colour became moderately red, and 2— 3% pepsindigested blood 

 solution. (The last constituent is possibly superfluous). On 

 this medium Pfeiffer's bacillus grew in pure culture but not 

 much better than on ordinary („cold" prepared) blood agar. In 

 the primary inoculations however the colonies were very well 

 developed, being about 2 mm. in diameter. This was un- 

 doubtedly due to a symbiosis effect from colonies of other 

 species of bacteria. In cases where the latter were only pre- 

 sent in small numbers it could be observed that the colonies 

 of Pfeiffer's bacillus were largest in their vicinity. In the 



