198 PLANT PHYSIOLOGY 



In all these four characteristics, catalyzers are seen to have 

 the same effect upon the reactions that oil does upon machinery. 

 Theoretically, the oil is not altered, it does not start anything, 

 the effect is proportional to the amount used (within limits), and 

 a small amount of oil may do a great deal of good. For these rea- 

 sons catalyzers may be called the lubricants of chemical reactions. 



Organic Catalyzers. — In test tubes, i. e., in vitro, the reactions 

 which are produced by catalysis may often be produced by heat- 

 ing, which also speeds up the reactions. In organisms, however, 

 the many processes which go on must be carried on at ordinary 

 temperatures; otherwise the protoplasm is injured. The high 

 temperatures produced in vitro cannot be produced in vivo. It 

 would hence seem very advantageous to the organism to produce 

 catalyzers which could bring about rapid reactions at ordinary 

 temperatures. Such catalyzers have been found in great quan- 

 tities and of many kinds, so that every conceivable kind of reaction 

 known to be necessary in the organism may have its own catalyzers. 

 To them have been given the name of enzymes, which may hence 

 be defined as organic catalyzers. The name means "in yeast" 

 (Gr., en zymos) and has been chosen because the fermentations 

 produced by yeast were among the first of such reactions to be 

 carefully studied. 



Organized and Unorganized Enzymes. — It was first thought 

 by Pasteur and the workers of his period that the fermentation 

 was a direct result of the action of the living yeast and that it 

 was a property peculiar to the yeast cells. Later it was found that 

 water extracts from sprouted barley seeds, from the stomach, 

 and from other tissues where sugars were broken down, had the 

 same property. Such extracts were called unorganized ferments 

 as opposed to the organized ones represented by the living yeast 

 cells. When Blichner, however, in 1897 showed that, by grinding 

 the yeast cells with sand and expressing the liquid under pressure, 

 he could obtain a liquid free from all living cells and which was 

 just as active as the yeast plant itself, all differences between organ- 

 ized and unorganized ferments disappeared. Instead one finds 

 the terms intracellular and extracellular enzymes. The former 

 are not secreted out of the cell, but the cell must be crushed in 

 order to secure the enzyme. These correspond to the "organized 

 ferments." The extracellular enzymes, on the contrary, are se- 

 creted by the cell into the liquid or into the intercellular spaces 



