CHAPTER IV. 
ENZYMES. 
68. Two Kinds of Ferments. 
As has been previously described, bacteria are the cause of 
the breaking-up of organic compounds into other compounds; 
as for example, milk sugar into lactic acid, or into alcohol and 
gas. Such changes or fermentations are termed organized fer- 
ments because they are the result of the growth of certain or- 
ganisms or germs. 
There is another class of changes which take place as a re- 
sult, not of bacterial growth, but of the action of a chemical 
substance known in contradistinction to the organized ferments, 
as unorganized ferments or enzymes. Such, for instance, is a 
substance found in the saliva known as ptyalin, which has the 
property of changing starch to sugar. In the stomach is found 
pepsin which has the property of changing solid proteids to 
soluble peptones, and in the pancreatic juices is found trypsin, 
another enzyme with properties similar to pepsin. These 
enzymes are secreted by the protoplasm of cells which make up 
the particular glands where they are usually found. Bacteria 
have this property of secreting enzymes, and as our knowledge 
of fermentations increases it may be found that the changes we 
now suppose to be due to the direct action of the living proto- 
plasm in the cells of plants and animals, are really due to 
enzymes secreted by the protoplasm. Enzymes have some char- 
acteristics in common in the manner in which they tehave under 
changes of temperature. They are most active at temperatures 
near blood heat (100° F.) and cease to act at low temperatures, 
while at high temperatures (150° to 200°) they are destroyed. 
The enzymes do not seem to be used up in their action, but will 
work over and over again. 5; 
34 
