46 AGRICULTURAL BACTERIOLOGY. 



action seems to differ from chemical actions in general in that 

 the ferment itself is apparently not used up in the process. 

 Whether this is strictly true may, from theoretical reasons, be 

 doubted, but at all events no direct evidence exists that they 

 are used up, and everything indicates that they can act indefi- 

 nitely. A very small amount of an enzyme may produce a 

 very large amount of chemical change, and the enzyme does 

 not appear to enter into the new chemical bodies in any degree 

 whatsoever. In some respects the enzymes resemble living 

 bodies, especially in their relation to heat, and the fact that 

 they are always produced by living organisms. But in other 

 respects they are sharply marked off from the organized fer- 

 ments. A long series of disinfectants, which wholly prevent 

 the action of organized ferments, have no influence upon the 

 enzymes. The latter do not increase by growth in the fer- 

 menting material, nor does their continued action depend upon 

 their nutrition. The distinction between these two classes of 

 fermentations has been clearly kept in mind in the develop- 

 ment of our knowledge of fermentation in the last half century. 



ORGANIZED AND UNORGANIZED FERMENTS REDUCED TO A 

 COMMON BASIS. 



The unorganized ferments or enzymes are always produced 

 by living organisms and are therefore fundamentally based' 

 upon living phenomena just as truly as are the organized fer- 

 ments. No enzyme occurs in nature except as produced by a 

 living animal or plant, and there seems to be no more prob- 

 ability of chemists being able to make enzymes than of their 

 making protoplasm. Some enzymes are produced by animals, 

 including ptyalin which changes starch to sugar, pepsin which 

 changes proteids to peptones, trypsin which has both functions, 

 rennet which curdles milk, etc. A large number are produced 

 by plants, such as diastase which changes starch to sugar, in- 

 vertin which changes cane sugar to dextrose or grape sugar. 



