260 VEGETABLE PHYSIOLOGY 
bark of Betula lenta, act on various glucosides, after the 
manner of emulsin. 
The digestion of the glucosides, we may notice, is always 
accompanied by the appearance of sugar, which is one 
of the products of their decomposition. The fate of the 
other bodies into which they split is not well ascertained, 
though there is some evidence that cyanogen compounds, 
even such as hydrocyanic or prussic acid, are used for 
nutritive purposes by certain plants. 
The digestion of fat or oil has not been very fully in- 
vestigated, though certain facts are known concerning 
its fate in germinating seeds. The digestion is generally 
accompanied by the appearance of starch grains in cells 
near the seat of digestion, and it was formerly considered 
that the starch arose directly from the oil. It appears 
now that the oil is split up by an enzyme, lipase, the result 
being the formation of a free fatty acid and glycerine. The 
subsequent decompositions are very complex, among the 
products being lecithin, a peculiar fatty substance containing 
phosphorus, as well as severai simpler acid bodies, which 
are crystalline instead of being viscid like the fatty acid 
first liberated. These pass into the general body of the 
seedling. The glycerine appears to contribute to the forma- 
tion of the lecithin. The decomposition is accompanied by 
the appearance of sugars and starch, which are probably 
formed by the protoplasm of the cells. 
The production of alcohol from sugar is brought about by 
another soluble enzyme, which has been prepared from 
yeast. Like the decomposition which is brought about by 
myrosin, the splitting up of the sugar is apparently not a 
process of hydrolysis. It may be expressed by the following 
equation : 
C6H120¢6 = 200, +- 2CH;CH,OH. 
In the reaction the sugar is decomposed, alcohol is formed 
and carbon dioxide given off. 
This enzyme, which has beeti called zymase, has been 
