70 



tion there. With a small magnification (x 50 — 100) characteristic 

 granulations are usually observed "in the central portion. 



4. No growth on haemoglobin-free media. For 

 the demonstration of this feature inoculation on ordinary agar 

 and agar with the addition of (blood-free) ascitic fluid is em- 

 ployed. 



5. The „s y m b i o s i s r e a c t i o n". On agar with the 

 addition of such a small quantity of dissolved haemoglobin 

 (i. e. haemolysed blood) that Pfeiffer's bacillus in pure culture 

 only grows scantily, the growth is increased to a considerable 

 degree round the colonies of other kinds of bacteria which 

 have been inoculated in the vicinity of the growth of Pfeiffer's 

 bacillus. 



6. 'T hcrate of growth. On media which are suitable 

 for the cultivation of Pfeiffer's bacillus there will always be 

 macroscopic colonies after 24 hours incubation at 37°, artd 

 after 48 hours there is not much more growth. (The reason 

 for introducing this character, in which indeed Pfeiffer's ba- 

 cillus does not differ from the majority of the ordinary bac- 

 teria which can be cultivated, is with view to distinguishing 

 it -from the whooping-cough bacillus which grows mluch more 

 slowly). 



In most cases all these 6 points are taken into account; 

 first an inoculation is made in Petri plates containing haemb- 

 globin-agar* (in a number of cases also on blood-agar)'; after 

 1 — 2 days in the incubator the colonies which have appeared 

 are examined microscopically (staining by Gram's method, 

 coiinterstaining with carbol-fuchsiri (Ziehl-Neelsen) diluted 1 -f D, 

 for 5 — 10 minufesX and also by subculture oh haemoglobin- 

 agar, blood-agar, and blood-free agar (ordinary agar, ascitic 

 agar or both); lastly the „symbiotic reaction" is carried* out. 



* Until June 1920 haemolysed blood was used for „haemoglobin", 

 and after that date pepsin-digested blood. * r 



For the • first month (July 1918) however, agar smeared with 

 a drop .of fresh human blood was used (as advised hy Pfeiffer 

 & Beck (1)). 



Concerning further details about the constitution and preparation 

 of the media the reader is referred to pp. 225 — 232. 



