204 OUTLINES OF BACTEEIOLOGY 



regards ferments as catalytic agents of complex constitution, derived 

 by secretion from a living cell. 



Ferments are not universally present at all times, but are secreted 

 only when they are required. Thus, whilst the ferment diastase is not 

 found in barley grains, it is present in malt. Again, in many cases, 

 perhaps in all, the organism first secretes a substance called mother-of- 

 ferment, which, later, is transformed into the ferment. Other names 

 for mother-of -ferment are preferment and zymogenes. These may be 

 found in resting seeds and in other parts of plants where nutriment is 

 stored. Thus pepsinogen, the preferment of pepsin, has been found in 

 the resting seeds of lupin, the pepsin itself not appearing until after- 

 germination. 



5. CLASSIFICATION OF FERMENTS. 



We may summarise what has been said above in the statement that 

 there are two kinds of ferments. 



(A) A secretion of an organism, which is able to carry on its 

 fermentative process quite apart from the organism which 

 produced it. Such secretions have been called unorganised 

 ferments, enzymes, and soluble ferments. 



(B) The living organism itself, working a fermentative change, 

 only during its own processes of growth, multiplication, etc. 

 Such organisms have been called organised ferments. 



It is most probable that several of the fermentations at present 

 assigned to the second class belong in reality to the first class, but that 

 it is owing to our insufficient knowledge that we have not yet been 

 able to extract the ferments from the cells. For instance, it was 

 supposed that the yeast fermentation belonged to the second class 

 until Buchner succeeded in demonstrating the presence of a ferment. 



Secretions of living organisms which set up fermentation. The 

 unorganised ferments which have been extracted may be classified as 

 follows : 



I. Ferments that change insoluble carbohydrates into soluble sugars. 

 Diastase (in various forms), which acts^on starch and its allies, 



changing them into dextrins and maltose. 

 Cytase, which decomposes cellulose. 

 Inulase, ,, ,, inulin. 



Seminase, ,, ,, mannose and galactose. 



Pectinase, ,, pectins. 



