§ VII.] Relation to the substratum. Enzymes. 7 1 



Many similar examples are to be found in works on fermen- 

 tation. 



The production of enzymes may also vary in the same form 

 according to the quality of the substratum. Wortmann (34) found 

 in the case of a Bacterium which he does not further determine, 

 that it excretes a starch-dissolving enzyme, and dissolves starch 

 if carbon is presented to it in the form of starch-grains only. 

 If the carbon is offered it in the form of a carbohydrate 

 which is readily soluble in water, such as sugar, or of tartaric 

 acid, the starch-grains which are offered to it at the same time 

 remain untouched. Similar facts are recorded of Bacillus 

 Amylobacter, which, according to van Tieghem, when fed with 

 glucose, leaves the cellulose which is presented to it at the same 

 time untouched, but decomposes it and takes it in as food if no 

 source of more readily assimilable carbon is available. 



Lastly, the definite activity of a particular species in the way 

 of fermentation or decomposition may be reduced to zero by a 

 change in the external conditions within the limits of vegetation, 

 even when the quality of the nutrient material remains the same. 

 Examples of this are furnished by the Mucorini already men- 

 tioned in passing, by the different species of Saccharomyces, 

 and by Bacillus Amylobacter and other Bacteria. Bacillus 

 Amylobacter, according to Fitz, loses the power of causing fer- 

 mentation, without losing that of vegetation, when exposed to a 

 high temperature, for instance, after the spores are boiled from 

 1-3 minutes in a solution of grape-sugar, or after being heated 

 for 7 hours up to 80° C. ; the same effect is produced if it is 

 cultivated during many generations with a copious supply of 

 oxygen in a nutrient solution, in which it is unable to excite 

 fermentation. The Mucorini present themselves in very dif- 

 ferent forms according to the change of conditions, though the 

 form is quite fixed in each particular case. Such a change of 

 form does not occur in Saccharomyces and the Bacteria which 

 have been more thoroughly examined as to this point, or only 

 to an inconsiderable degree. That external conditions of every 



