UNORGANISED FERMENTS 267 



groups, the four most important of which are the follow- 

 ing: 



(1) The Diastatic Ferment. 



(2) The Peptic Ferment. 



(3) The Eennet Ferment. 



(4) The Pancreatic Ferments. 



The action of the first class appears to be due to the 

 presence of one or more living cells in a body ; the action 

 of the second may be traced to the molecules of which they 

 are composed, and which are the carriers of the chemical 

 force that causes the changes. The second class of ferments 

 will only be dealt with here. 



1. Diastatic Ferment. — The best-known instance of this 

 occurs in extract of malt. If a solution of extract of 

 malt be heated to about 30° C. with its own weight of 

 starch in solution, the starch is completely converted in 

 a few minutes into maltose and dextrine, and ceases to 

 answer the iodine reaction. The diastatic fermentation 

 occurs to a small extent in the saliva. The diastatic body 

 may be obtained by filtering saliva, and mixing with five 

 or six times its weight of alcohol. The very slight pre- 

 cipitate which falls is dried at the temperature of the air. 

 It has a strong diastatic action. 



The diastase of malt is capable of converting no less 

 than 2,000 times its weight of starch. The change can be 

 illustrated by the following equation : 



eCeHioO^ + 4H,0 = 2C«H,„05 + 2(Ci,H,,0n + H^O) . 

 Starch. Dextrin. Maltose. 



2. Peptic Ferment. — This fermentation takes place in the 

 stomachs of animals when food is digested, and the stomachs 

 are the sole source of pepsin. 



Various theories of digestion have been advanced from 



