270 VEGETABLE PHYSIOLOGY 



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 quite recently the 

 alcoholic fermentation of sugar was attributed to such an 

 action in the yeast-cell, and in the cells of certain 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 Myco- 

 derma or Bacterium aceti. Similar protoplasmic action is 

 responsible for the production of various acids in the cells 

 of the higher plants. The dependence of these fermenta- 

 tions 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 their 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 proteids and sugars. 

 The former will be thrown down with the enzyme by the 

 alcohol. 



