CATALYSIS AND ENZYMES 301 



optically active substances. Glucose is dextro-rotatory and we find that, as 

 glucoside is formed, the rotation of the mixture diminishes, finally passing to the 

 laevo-side of zero. Now there are two possible optical isomers of the glucoside, 

 according to the position of the glyceryl group in relation to the terminal hydrogen 

 atom of the glucose. Thus, diagrammatically, putting G for glyceryl : 

 GO H H OG 



-C C 



/ ! / 



/ HO-C-H / HO-C-H 



0| O I 



X HO-C-H X HO-C-H 



X C H ^C-H 



HO C-H HO-C H 



HO C= H 2 HO-C=H. 2 



a-glucoside. /3-glucoside. 



The one on the left, called for convenience the a-glucoside, has a higher dextro- 

 rotation than glucose, while the /2-glucoside is laevo- rotatory. The preparation 

 from almonds, which was used in the experiments, is found to cause hydrolysis 

 of the series of /3-glucosides only, of which there are a great number. The 

 experiment quoted shows that it also brings about synthesis of the ft- form 

 of the glycerol-glucoside, since that one formed is Isevo-rotatory. Similar results 

 were obtained by Bourquelot and Bridel (1913) in the case of numerous glucosides 

 of alcohols. Note that the two glucosides are not mirror-images (see page 284 above). 

 An important fact, which will be found to be of much significance in later 

 pages, is that the reaction takes place in alcohol of such a strength that the agent, 

 emulsin, is completely insoluble in it and can be filtered off, leaving no trace 

 in solution. The same statement applies to the experiment of Dietz with extract 

 of pancreas, or lipase, as the active constituent has been called. 



What is the meaning of all these facts ? 



To begin with, it will have been plain from the facts given in the chapter 

 on Nutrition that the chemical changes which take place in the living organism 

 are of a kind such as, in the laboratory, can only be brought about by powerful 

 reagents and high temperatures. Take the hydrolysis of protein to amino-acids. 

 This is effected in the laboratory by boiling concentrated hydrochloric acid, but 

 in the organism it takes place, at an equal rate, at ordinary temperatures and 

 in a medium which is only just faintly alkaline or neutral. This fact especially 

 attracted the notice of Schonbein (1863). 



Berzelius (1837, pp. 19-25), however, directed the attention of chemists to 

 what he called a " force which differs from those hitherto known." On account 

 of the importance of the question, I will give, in an abbreviated form, the 

 description given by Berzelius, whose portrait is reproduced in Fig. 82. 



The difficulty to which attention has just been called, is pointed out by 

 this chemist. Blood is supplied to an organ and, without the assistance of 

 any other liquid, we obtain saliva, milk, urine, arid so on. A discovery was 

 made by Kirchhof (1812) which gave the first clue to an understanding of the 

 vital processes, but which, as it is scarcely necessary to remark, are still far 

 from complete explanation. Kirchhof found that starch could be converted 

 into glucose by the action of dilute sulphuric acid, which was itself unchanged 

 in the process, since it could be recovered at the end. The next step was, 

 according to Berzelius, the discovery of hydrogen peroxide by Thenard. This 

 was noticed to be decomposed, not only by soluble alkalies, but also by many 

 various kinds of solid insoluble substances, such as manganese peroxide, silver, 

 platinum, and the fibrin of blood. These do not take part themselves in the new 



