340 A GELATIN-HARDENING BACTERIUM, 



the bacterium that was capable of diffusing through gelatin and 

 either directly or indirectly affecting it. The darkening of the 

 medium was probably a phenomenon connected with the 

 hardening. 



Bearing in mind the action of tannin upon gelatin, I thought 

 it possible that some of the constituents of the medium might 

 have been altered to tannin and the darkening caused by traces 

 of iron salts. This, however, did not prove to be the case, for 

 the addition of ferric chloride to a tube of the molten medium 

 before the hardening had proceeded far showed no reaction. 

 Fluid cultures contained no formaldehyde, so that this substance 

 is probably absent in the cultures on solid media. 



Believing that the mahogany colour might be caused by an 

 oxidase acting upon traces of tyrosin in the medium, I added 

 tyrosin to nutrient gelatine and at the same time tried the effect 

 of different sugars, etc., and noted the appearances at the end of 

 9 and 28 days. With saccharose, mannit, lactose and levulose 

 the growths were good, the medium slowly liquefied, and only a 

 trace of colour was produced. With tyrosin the nutrient gelatin 

 showed a slight tinge of brown in the upper layers, but the colour 

 disappeared. With galactose, dextrose, and dextrose-tyrosin, 

 the growth was scanty and the medium became deep brown in 

 colour, especially in the middle layers; there was a very slight 

 liquefaction; a single drop of fluid rested at the lower end of the 

 stroke on the 28th day. As no increase of colour resulted from 

 the addition of tyrosin to dextrose, and as the colour that 

 developed in the tube with tyrosin-nutrient gelatin was faint, it 

 is probable that the production of colour is not due to the forma- 

 tion and oxidation of tyrosin by the bacterium. Oxidising 

 enzj^mes were sought for by adding an alcoholic solution of gum 

 guiacum to the glucose-gelatin before sterilisation. The medium, 

 after infection, behaved as glucose-gelatin; the brown colour was 

 obtained without a trace of blue, which is characteristic of the 

 oxidising enzymes. 



The partial liquefaction of the gelatin leads us to infer that 

 there are two agents at work, one hardening, the other liquefying 



