42 BIOLOGY AND TECHNIQUE 



exclusive and specific parts played by various microorganisms in these 

 processes. While the observations and deductions made by Pasteur have 

 not been greatly modified, a large store of information has been gained 

 since his time, which has thrown additional light upon the chemical de- 

 tails and the more exact manner of action of the factors involved. 



The actual work of cleavage in both fermentation and proteid cleav- 

 age is carried out by substances known as enzymes or ferments, the nature 

 of which we must further discuss before their manner of action can be 

 fully comprehended. 



Bacterial Enzymes or Ferments. — A ferment or enzyme is a substance 

 produced by a living cell, which brings about a chemical reaction with- 

 out entering into the reaction itself. The enzyme itself is not bound to 

 any of the end products and is not appreciably diminished in quantity 

 after the reaction is over, although its activity may be finally inhibited 

 by one or another of the new products. The action of bacterial enzymes is 

 thus seen to be closely similar to that of the chemical agents technically 

 spoken of as " katalyzers," represented chiefly by dilute acids. Thus, 

 if an aqueous solution of saccharose is brought into contact with a 

 dilute solution of sulphuric acid, the disaccharid is hydrolyzed and is 

 decomposed into levulose and dextrose. 



Thus: 



Ci2 H.i2 Oil + H, O =^ Co Hi2 Og -1- Co Hi2 Og 

 In contact with Dextrose Levulose 



dilute H2SO4 



During this process, which is known as " inversion," the concentration 

 of the sulphuric acid remains entirely unchanged. While theoretically 

 the changes brought about by enzymes and katalyzers are usually 

 such as would occur spontaneously, the time for the spontaneous oc- 

 currence would be, at ordinary temperatures, infinitely long. The defini- 

 tion for enzymes and katalyzers is given by Ostwald, therefore, as 

 " substances which hasten a chemical reaction without themselves taking 

 part in it." Exactly the same result which is obtained by the use of dilute 

 sulphuric acid is caused by the ferment "invertase" produced, for 

 instance, by B. megatherium. Were a solution of saccharose sub- 

 jected to heat, without katalyzer or ferment, a similar change would 

 occur, but by the mediation of these substances the inversion is pro- 

 duced without other chemical or physical reinforcement. 



This analogy between enzymes and katalyzing agents is very 

 striking. Thus, as stated, both katalyzers and enzymes bring about 



