IX 



Nocggerath ) showed that by cultivating bacteria on 

 gelatine stained with dyes, the colours of which resem- 

 bled those of the spectrum, each microbe selected its 

 specific colour. 



Behring 7 ) found, that by the use of litmus agar, it 

 was possible to distinguish between a weakly and a 

 highly virulent anthrax strain, owing to the greater reduc- 

 ing power of the former. 



Kitasato and Weyl 8 ) showed, by the use of indigo 

 blue, that certain anaerobes (B. tetanus) were capable 

 of absorbing oxygen. 



Notwithstanding the variety of ways in which colou- 

 red media have been employed, they have doubtless been 

 of most service in differentiating B. typhosus and B. 

 coli, as will be seen from the following brief summary. 



Gasser 9 ) found that B. coli in stroke culture on fuch- 

 sin agar would decolourise this sooner than B. ty- 

 phosus. 



Wi'niz 10 ) availed himself of a solid medium containing 

 lactose and litmus to differentiate the two bacilli. 



Uffelmann 11 ) proved by means of methyl-violet gela- 

 tine acidified with citric acid that B. typhosus took up 

 the blue colour, so that the colonies were on this account 

 well defined. 



Sommaruga 12 ) took advantage of different media con- 

 taining rosolic acid, and regarded the decoloration pro- 

 duced by B. typhosus as due to a reduction, since it 

 occurred even if the medium remained alkaline. 



Marpmann 13 ) employed malachite-green sulphite agar 

 on which B. coli gives a gray and B. typhosus a green 

 growth, the latter being due to the production of an 

 aldehyde. 



Kashida 14 ) made use of a 2 % lactose agar containing 

 urea and litmus, in which medium B. coli at first pro- 



4 



