ENZYMES AND FERMENTS 125 



of insoluble substances to take up water, and to split up 

 into simpler molecules of a different composition and 

 soluble in water. There are no gaseous by-products. 



According to Went the secretion of enzyme by Manilla 

 sitophila is influenced by nutrition. Food rich in carbo- 

 hydrates promotes the formation of the greatest amount of 

 enzyme. The quantity of such food also exercises an 

 influence, and an excessive quantity checks the secretion. 

 This author does not accept the general opinion that the 

 secretion of an enzyme indicates the lack of certain nutrients, 

 or cell-starvation. Ward has shown that it is by means of a 

 minute drop of enzyme, secreted by the tip of a hypha, 

 that the latter is enabled to penetrate the walls of living 

 cells of the host-plant. Biffen has demonstrated the 

 presence of a fat destroying enzyme in a fungus, probably 

 a species of Nectria. In this instance the enzyme acted by 

 first emulsifying the fat of cocoa-nut endosperm, and then 

 splitting it up into a fatty acid and glycerine. 



Certain glucosides, as salicine, amygdaline, coniferine, 

 and aesculine, are broken up by enzymes, and yield among 

 other products glucose, a sugar that can be directly assimi- 

 lated by fungi. 



Wehmer founded a genus called Citromyces for certain 

 fungi capable of changing carbo-hydrates into citric acid. 

 The production of this acid is due in the first place to the 

 oxidation of the carbo-hydrate, and is dependent on the 

 presence of oxygen. The most favourable nutrient solution 

 for its formation is a moderately strong solution of sugar. 



Organic ferments agree with enzymes in being able to 

 effect chemical changes in organic substances, but differ 

 materially in the fact that such changes can only be induced 

 under the influence of the living cells producing the ferment. 



