ENZYMES 37 



bitter controversy raged during the late eighteenth and 

 the nineteenth centuries as to whether or not such fer- 

 mentations were due to living entities. Berzelius in 1837 

 put forward the suggestion that the processes were due 

 to catalysts, whilst Liebig considered that putrefaction 

 and similar processes were due to vibrations set up by the 

 disintegration of living cells. It fell to Pasteur, about 

 1870-75, to show that all these processes were associated 

 with the vital processes of minute living organisms, 

 yeasts, bacteria and fungi, and that if the life of the 

 micro-organism was destroyed (by heating, for instance) 

 then the fermentations were brought to a standstill. 

 Pasteur described the responsible micro-organisms as 

 " organised ferments." 



Parallel with this controversy various digestion and 

 breakdown reactions by plant and animal juices and 

 extracts were being described. Substances were isolated 

 from such extracts which could bring about the same 

 reactions in the test-tube. For instance, Plane he in 1810 

 had observed that solutions of guaiacum were turned 

 blue by extracts of certain roots (this is perhaps the first 

 recorded isolation of an enzyme) ; amygdalin had been 

 shown to be hydrolysed by an extract of bitter almonds 

 from which Liebig and Wohler prepared the enzyme 

 emulsin ; Payen and Persoz showed in 1832 that starch 

 was hydrolysed by the enzjrme diastase, which they 

 obtained by precipitation of barley malt extracts with 

 alcohol ; the protein degrading preparations pepsin and 

 trypsin had been obtained from the gastric juice and 

 from the pancreatic juice respectively. The behaviour 

 of these and other substances like them was recognised 

 as being similar in many respects (such as ready destruc- 

 tion by heat) to the action of the " organised ferments," 

 and they came to be known as " soluble " or " unorganised 

 ferments." Then followed a long discussion as to whether 

 there was any essential difference between the organised 



