8 June, 1907.] Elements of Animal Physiology. 337 



THE ELEMENTS OF ANIMAL PHYSIOLOGY. 



TF. A. Osborne, M.B., D.Sc, Professor of Physiology and Histology, 

 Dean of the Facidtv of Agriculture in the University of Melbourne. 



{Continued from page 2jj.) 



CHAPTER VI. 



The Enzymes. 



The changes denoted bv the word fermentation have long l)een a 

 mystery to the human mind. The most familiar example of this process 

 is the transformation of sugar into alcohol and a gas (carbon di-oxide) 

 bv the action of yeast. The salient feature in all fermentations is the 

 large amount of substance which is changed bv a small amount of ferment 

 without anv loss of power being incurred by the ferment. To explain 

 this mystery many crude theories have been put forward from time to 

 time such as the philosophers' stone, spiritual agency, &c. The great 

 I-iebig fell into the blunder of regarding it as a simple chemical trans- 

 formation unconnected in any way with life. It was the brilliant work 

 of Pasteur that proved conclusivelv that yeast was a living thing — a 

 plant in fact. He showed that putrefaction was caused by living bac- 

 teria and that the souring of milk and kindred changes were due to living 

 things. Before Pasteur's discovery a few observations had been made 

 on certain products of living things, but themselves not living, which 

 could produce changes allied to fermentation. Thus, in the saliva, a 

 ferment W'as discovered which, though present in minute amounts, could 

 transform large quantities of starch into sugar. In the gastric juice a 

 ferment pepsin was found which, in conjunction with an acid, could 

 digest protein. Independentlv of these workers the chemists had dis- 

 covered a number of reactions in which small amounts of substance could 

 produce changes in immensely greater quantities of other substances with- 

 out themselves undergoing any change. Thus it was found that hvdrogen 

 and oxygen would unite almost instantaneouslv in the presence of a minute 

 amount of platinum, the platinum remaining unaffected and capable of 

 producing the same change apparently for all time. To such reactions 

 the name contact reactions was given and later the name catalysis. The 

 number of catalytic reactions known to the modern chemist is very great 

 and catalysis is being more and more employed in the laboratory and 

 manufactory. But the mere naming of a reaction did not do away with 

 the mystery. A step in the solution of this problem was made when it 

 was shown that in all catalytic reactions the essential feature is a 

 hastening, an acceleration of a change w^hich is normally going on but 

 in a very slow manner. Hvdrogen and oxvgen mixed in a test-tube at 

 ordinary temperatures are reallv uniting to form water, but the change 

 is so slow that the life time of a man would be insufficient to show any 

 appreciable diminution in bulk; introduce a tinv speck of spongy 

 platinum and the reaction is over in a fraction of a second. Hydrogen 

 peroxide is continuously decomposing into oxygen and water but at a 

 slow rate ; introduce a drop of water in which finely divided platinum is 

 floating and the decomposition gains enormously in rate even though the 

 amount of platinum added can only be expressed in millionths of a grain. 



