34 PROTOPLASM AND THE CELL 



was given as early as 1836 by Berzelius when he discovered the 

 action due to what he called " catalytic force." Subsequent 

 researches have shown that his catalyzers, which we now know 

 as enzymes, are chemical substances which participate in 

 chemical reactions by forming compounds of unstable and inter- 

 mediate character. The compounds break down easily thus 

 freeing the enzymes and enabling them to repeat the process 

 so that they appear to be unaltered by the reactions which 

 they undergo. 



Fermentation. The most exhaustive study of an enzyme has 

 been on that which produces alcoholic fermentation early traced 

 by Pasteur to yeast cells. Substances producing fermentation 

 were called ferments, the name being due probably, to the 

 generation of gas during the process of alcohol formation, caus- 

 ing the sugary fluid to froth or foam. In the i6th century all 

 processes involving the generation of gas were considered in- 

 stances of fermentation, but step by step advances were made 

 until the latter part of the igth century saw the complete inter- 

 pretation of the phenomenon. In the iyth century a distinct- 

 tion was drawn between the gas generated and the permanent 

 product alcohol, remaining behind. It was also shown that 

 this gas mnorum and carbonic gas are the same. Later it was 

 demonstrated that alcohol is a newly formed product of the 

 fermentative action, and finally, in the lyth century again, a 

 distinction was drawn between alcoholic fermentation and acid 

 fermentation or frothing which occurs during the action of 

 acids on carbonates. It was at this period that Stahl showed 

 that a small quantity of matter undergoing decomposition if 

 added to another quiescent body, will cause the latter to decom- 

 pose, thus giving a hint of the infective nature of fermenting 

 liquid. Boerhaave came to the conclusion that only vege- 

 table matter undergoes fermentation while animal matter 

 putrifies. 



With Lavoisier chemistry became a more exact science and 

 in alcoholic fermentation it was found that the sugar disappears 

 while alcohol and carbonic acid are newly formed bodies, i.e., 

 that sugar breaks down into alcohol and carbonic acid with a 



