164 



dark colouration of the medium' caused by a rather easily 

 diffusing substance (oxidation product of the hydroquinone, 

 splitt off). 



Investigation of the Proteolytic Power. 



In Dec. 1920 all the strains on p. 110 (except I 1, and I 38) 

 were inoculated on peptone broth gelatine (containing a 

 little over l<y gelatine), to which was added about 2% dissolved 

 blood corpuscles. The tubes were incubated for a week. In 

 most cases a good growth appeared. At the end of the week 

 the tubes were cooled. In each case the gelatine set just as 

 firmly as before inoculation. 



The same strains were also tested as to their power of 

 liquefying coagulated serum. The following medium was 

 used. One part salt-free and sugar-free peptone broth in double 

 concentration was mixed with 3 parts of ox serum 1 , to which 

 was added pepsin-digested blood in the usual concentration. 

 This concoction was poured into Petri plates and coagulated 

 by a short heating to 70°. Pfeiffer's bacillus grew splendidly 

 on this medium. In no case was the slightest sign of liquefac- 

 tion of the serum observed after a week in the incubator. 



Indol Formation. 



The absence of proteolytic power on the part of Pfeiffer's 

 bacillus in the ordinary meaning of the word, does not mean 

 that it is unable to decompose dissociation products of the 

 proteins. 



A dissociation which has particularly attracted the atten- 

 tion of bacteriologists is the liberation of indol from the trypto- 

 phane molecule. 



According to Frieber all bacteria can split off the group 

 CH.NrL, from tryptophane, which is seen on the extreme right 

 in the formula below, while comparatively few organisms can 

 break the bond marked with an asterisk, which liberates indol 

 and which can be detected by Ehrlich-Bohme's reaction. (The 



