THE YEASTS CHAPMAN 311 



acceleration of fermentation by the addition of aldehydes is niiich 

 greater in the expressed yeast juice than in the case of the living cell, 

 and there are other respects in which the actions proceeding in the 

 juice differ from those occurring within the cell. This i-eems to 

 suggest that the mechanism of fermentation is in some way directly 

 connected with the organized structure of the cell. In the living 

 cell, again, the velocity of fermentation is much greater than in 

 the expressed juice, and it would seem that in its natural surround- 

 ings within the cell zymase is free to act without the disturbing 

 influences wdiich probably exist in the expressed juice where all the 

 cell contents are mingled, and some substances may well interfere 

 with the activity of others. 



Cramer (Proc. Roy. Soc, 1915, 88, B, 584) has dealt with this 

 important and interesting point, and has shown that the most 

 striking difference between the action of enzymes within the living 

 cells and their action after extraction is the extreme sensitiveness 

 with which, in the former case, they respond to very slight changes 

 in the surrounding medium, being sometimes retarded, sometimes 

 accelerated, and sometimes reversed. According to Cramer surface 

 tension would appear to be an important factor, such surface tension 

 being operati>'e, for example, at the periphery of the cell and at 

 the boundaries of the nucleus, vacuoles, granules, colloidal aggre- 

 gates, etc. Thus the conditions for enzyme action may be very dif- 

 ferent in one part of the cells from those occurring in another part. 

 Under the influence of very slight changes in external conditions 

 there inaj, for example, take place within the cell a movement of 

 the cytoplasm, or changes in the concentration of the cell constituents 

 which, by altering the surface tension at different parts, may al- 

 together change the conditions for enzymic action. Even assuming 

 Cramer's explanation to be correct, it still means that the great 

 variations in the physiological and chemical activities of the cell 

 are dej^endent on internal structure, and it is to this problem that 

 future research may usefully be directed. Any great increase in 

 our Imowledge of this subject might prove to be of the highest im- 

 portance, not merely in regard to industrial operations, but as af- 

 fording a deeper insight than we yet possess into the true character 

 of the vital activities ot the living cell. It may be hoped that our 

 society, which has done so much to direct and foster the study of 

 microscopical science, may figure prominently in connection with 

 an investigation, the results of which might well prove to be of 

 fundamental importance. In the living cell we have, in fact, a 

 chemical laboratorj^ of the highest efficiency, and of the most re- 



