72 BACTERIAL METABOLISM ENZYMES 



considered to be in a state of unstable equilibrium or decomposi- 

 tion. This is communicated to its surroundings, producing chemical 

 changes. This was opposed by Pasteur and Tyndall who showed 

 that in the absence of microorganisms fermentation does not take 

 place. 



There were certain changes which they proved to be due to 

 bacteria and yeast; others which were brought about by pepsin, 

 tripsin, etc. This led to the classification of ferments as organized 

 and unorganized. Under organized ferments were grouped such 

 substances as some bacteria and yeasts, which, when examined 

 under the microscope, possess a definite organized structure and 

 which act by virtue of vital processes. The unorganized ferments 

 included amylase, pepsin, rennin, etc., and were described as 

 "non-living unorganized substances of a chemical nature." Kiihne 

 designated this last class of substances, enzymes. This classifica- 

 tion into organized and unorganized ferments was generally accepted 

 and practically unquestioned until overthrown by Biichner (1897) 

 in his epoch-making investigation of yeast. He carefully mixed 

 1000 grams of brewers' yeast with an equal weight of quartz sand 

 and 250 grams of infusorial earth generally known as Kieselguhr. 

 This mixture was ground together until plastic; 100 c.c. of water 

 was added and wrapped in a press cloth and filtered in a press cap- 

 able of exerting a pressure of from 400 to 500 atmospheres. The 

 juice was clarified by shaking with Kieselguhr and filtering. The 

 liquid so obtained is slightly heavier than water and possesses a 

 pleasant odor. On boiling, a quantity of proteinaceous matter 

 separates and the liquid becomes nearly solid. 



The unboiled juice possesses all the power of the yeast cell in so 

 far as fermentation is concerned. However, the action is not 

 stopped by chloroform nor by the passage of the liquid through a 

 Berkefeld filter nor through a dialyzing membrane. The enzyme 

 which is present in the solution has been termed by Biichner 

 zymase. Later the lactic acid- and the acetic acid-producing bacteria 

 were subjected by Biichner to similar treatment to that given the 

 yeast cells, and the active intracellular enzymes were obtained. 

 Since that time the list of unorganized ferments or enzymes has 

 continued to grow at the expense of the organized ferments until 

 it is generally conceded today that all fermentations are due to 

 enzymes, there being only this difference that some are formed 

 and readily diffuse out of the body of the cell during its life and are 

 known as extracellular ferments, whereas others remain in the cell 

 and are known as intracellular ferments. 



Definition of Enzymes. Enzymes have been defined as "unor- 

 ganized, soluble ferments, which are elaborated by an animal or 

 vegetable cell and whose activity is entirely independent of any 

 of the life processes of such a cell." 



