Glucose and Mannitol hy B. coli communis. 10 S 



that the nature of the fermentation products, and the proportion in which 

 these appear in the final analysis, will depend on the extent to which the 

 various enzyme actions co-operate, which in turn depends on conditions 

 sucli as concentration of salts and temperature. It has been shown also 

 that the synthetic side of the process of bacterial fermentation is quanti- 

 tatively of the same order as the decompositions which follow. 



Some of these facts have so far been hidden because the various changes 

 occur rapidly, and previous experiments have been too prolonged to serve 

 for their investigation. In the light of these results it is of interest to 

 consider what the objections are to prolonged fermentations if such experi- 

 ments aim at a characterisation of the enzymes of any particular organism 

 at any particular time. For it is important to insist that a organism is not 

 constant as regards the enzymes it contains, but that its composition in 

 this respect will depend upon its immediate past history, and thus only a 

 superficial idea of the fermentation processes set up by the organism is 

 given by a study of the action as a whole, and it is necessary, in order that 

 any true imiformity should be obtained, that the actions of the separate 

 enzymes should be studied. 



The objections are as follows : — 



(1) The strain of the organism introduced at the start may vary with the 

 production of new enzymes. 



(2) Even if the enzymes remain constant in kind and amount their actions 

 may be selectively impeded by the conditions of the experiment at the start, 

 or by the accumulation of the products of the fermentation. 



(3) Even if the enzyme actions were unimpeded by the conditions 

 imposed, the prolougation of the experiment would give nothing but the 

 sum of the various actions concerned. 



For, if an organism be introduced in a small seeding into an artificial 

 medium, the enzymes which are developed in the subsequent generations 

 of the organism may not necessarily be the same as those which were 

 present at the start. There may be adaptation to the conditions in the 

 sense of the production of enzymes which bring about the decomposition 

 of the substance under investigation along simpler lines. As an example 

 of such a selection taking place during a single fermentation experiment, 

 it will suffice to refer to an observation made by the writer in an earlier 

 communication, namely, that after the fermentation of mannitol by certain 

 strains of B. coli commvnish.9.(i come to a standstill as regards the produc- 

 tion of gas, the strain which could now be isolated from the solution differed 

 from the original strain in that it now no longer produced gas from mannitol 

 even when inoculated into a fresh solution. 



