THE METABOLISM OF PLANTS. 193 



than the action of the ferment. With the foregoing observa- 

 tions those of Brown and Heron and of Atkinson are doubt- 

 less to be connected. Brown and Heron' observed that the 

 diastatic action of malt-extract is much increased after the 

 addition of Yeast, and Atkinson has made similar observa- 

 tions on rice when attacked by a certain Mould (apparently 

 a Eurotium). It appears from all these facts that the forma- 

 tion of the ferment depends upon the decomposition of some 

 mother-substance, a zymogen, probably a proteid. This de- 

 composition is promoted in an organ by the presence of an 

 acid, and by the presence of oxygen ; when the zymogen has 

 been extracted from the organ (as in the case of malt- 

 extract), or when the organ has been killed (rice), it may be 

 effected by another organism altogether. 



The ferments may be obtained by the following methods. Baranetzky 

 extracted the N seeds or other parts of plants with water for about half an 

 hour; if much fat or chlorophyll were present the material was first 

 extracted with a mixture of ether and alcohol, then pressed and left to 

 dry ; the watery extract was filtered and then precipitated with strong 

 alcohol ; when the precipitate had collected the alcohol was decanted, 

 and the precipitate was washed with weaker alcohol (about 85 per cent.) 

 to remove all traces of sugar ; the precipitate was collected on a filter 

 and treated with water ; the clear filtrate contained the ferment in solu- 

 tion. Another method is to extract the material with glycerin, after 

 having treated it for 48 hours with strong alcohol ; the glycerin-extract is 

 then to be strained and allowed to drop into a tall cylinder containing a 

 mixture of 8 parts of alcohol to I of ether ; a precipitate is formed which 

 is to be kept for some days in alcohol, and then treated with glycerine 

 which dissolves the greater part of it ; the glycerin-solution is then 

 precipitated as above by alcohol, the precipitate being the nearly pure 

 ferment which was readily soluble in both glycerin and water. It was by 

 this method that von Gorup-Besanez attempted to extract ferment from 

 seeds (see p. 173), but it is doubtful if he extracted anything but peptone. 



But there are certain chemical changes which we are 

 unable to account for in either of the above-mentioned ways : 

 these are the fermentations, which we usually associate with 

 the life of lowly Fungi, such as Yeast and Bacteria. It is 

 difficult to believe that the sugar which is decomposed by 

 Yeast into carbon dioxide and alcohol, that the alcohol which 

 is converted into acetic acid by the Mycoderma Aceti, that the 

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