262 VEGETABLE PHYSIOLOGY 



sugar, can peptonise proteins, and carry out other digestive 

 processes, without the intervention of an enzyme. Though 

 this property can easily be proved in the case of cells of 

 the higher plants, it is especially prominent in many of the 

 more lowly organisms such as the Bacteria. The processes 

 of putrefaction generally depend on this property in the 

 organisms which bring it about. Till the discovery of 

 zymase the alcoholic fermentation of sugar was attributed 

 to such an action in the yeast-cell, and in the cells of cer- 

 tain ripe fruits under particular conditions, the chief of 

 which was the deprivation of oxygen. Such an action 

 leads to the formation of acetic acid from alcohol by the 

 microbe Mycoderma or Bacterium aceti. Similar proto- 

 plasmic action is responsible for the production of various 

 acids in the cells of the higher plants. The dependence 

 of these fermentations on the vital activity of the 

 protoplasm is evident from the fact that no enzyme can 

 be extracted from the cells which can set up the particular 

 changes in question. 



It is not difficult to prepare the enzymes from the tissues 

 in which they work, but it would be extremely rash to 

 say that they are in anything like a pure condition when 

 obtained. Nor is it easy to say much about the purifica- 

 tion, as they are not known except in close connection with 

 the substances on which they act, or with the products of 

 the decompositions they initiate. There is therefore no 

 known test of their purity. 



They can be extracted by treating the tissue, which 

 should be very finely divided or ground in a mortar, with 

 glycerine, or with a solution of common salt, or with water 

 containing a trace of an antiseptic. After a period of ten 

 or twelve hours the extract should be strained and subse 

 quently filtered, when the enzyme may be precipitated from 

 the filtrate by adding strong alcohol. It is very evident 

 that this process will not yield it pure, for the solvents 

 employed will dissolve many constituents of the tissue 

 besides the enzymes, particularly proteins and sugars. 





