46 A. Killen Macbeth on 



Part. III. 

 Natural Catalysts or Enzymes. 



Having examined the behaviour of catalysts and reviewed 

 some cases of the application of catalysis in manufacturing 

 operations, association of ideas carries one on to ask the question, 

 Are any substances found in nature which function, or can 

 function, as catalysts'? Many substances are found elaborated in 

 the presence of living organisms which assist definite chemical 

 reactions occurring in the animal body, and doubtless also 

 effect the changes that take place during the plant growth. 

 Grain is largely made up of starch, but there is also present a 

 substance known as diastase. The diastase can be developed 

 by moistening the grain and allowing it to sprout. If the grain 

 is subsequently crushed and allowed to stand in contact with 

 water the diastase assists the breakdown of the starch into 

 sugars. This is known as hydrolysis^ water being added on to 

 the starch, thereby converting it into sugar. This conversion of 

 starch into sugar does not ordinarily take place, but it may be 

 brought about in the laboratory by boiling the starch for some 

 time with dilute sulphuric acid : the acid acts as a catalyst, 

 inducing the addition of water. We are, therefore, brought face 

 to face in these changes with the great contrast between the 

 violent action of an inorganic catalyst and the quiet, steady 

 working of the natural ferment, diastase. 



Another example of natural ferments — or enzymes as they 

 are called — is seen in the case of almonds. Almonds, when 

 freshly ground, do not possess their characteristic odour. This, 

 however, develops in the course of time and is due to the chemical 

 change brought about by the enzyme emulsin which is present. 

 From the almonds a substance known as amygdalin can be 

 extracted which, when moistened and treated with emulsin, 

 breaks down into sugar (glucose), prussic acid and oil of bitter 

 almonds (benzaldehyde) to which is due the characteristic smell. 



