SYNTHESES BY ENZYMES 365 



its components by diluting a sample to 50 c.c. and adding 

 half a gram of fresh emulsin. In about two to three days the 

 hydrolysis will be complete, and the original rotation will be 

 restored. As commercial emulsin is, however, itself laevo- 

 rotatory, a control experiment should be made with emulsin 

 alone or else the emulsin may be precipitated by adding 

 mercuric nitrate, and filtering before the polarimeter reading 

 is made. 



In a subsequent investigation * Bayliss found that actually 

 very little arbutin was formed, but that the glucoside really 

 produced was that of glycerol. That being so, the hydro- 

 quinone can be left out of the mixture, and as a result the 

 sealing of the tubes and subsequent treatment with sodium 

 bisulphite is rendered unnecessary. The best mixture is 

 made as follows: Glucose (anhydrous) 18, water 12, glycerol 

 40, and emulsin 3 parts by weight. The glucose must be 

 dissolved in the water and cooled before adding the glycerol, 

 owing to the production of glycerol glucoside by heat. At 

 a temperature of 47 a diminution of rotation from + 2'83 

 to + o'8o takes place in seven days, and equilibrium at 

 - o'i6 (corresponding to about 75 per cent synthesis) is 

 practically attained in fifteen days. 



The experiment is of interest with regard to the theory of 

 catalysts, since if the above mixture of glycerol, hydroqui- 

 none and glucose is heated without enzyme to 100 for some 

 hours a certain amount of glucoside synthesis results ; it may, 

 therefore, be assumed that some synthesis also takes place, 

 though very much more slowly, at 38. The emulsin, there- 

 fore, in accordance with Ostwald's definition of an enzyme, 

 merely accelerates a reaction which is already taking place, 

 though very slowly. 



A CONSIDERATION OF CERTAIN TYPES OF ENZYMES. 



Before passing on to a more special consideration of indi- 

 vidual enzymes, attention must be drawn to a point of general 

 application to all enzymes. It is of the highest importance that 

 experiments on enzymes which take several hours to carry out, 

 should be conducted under aseptic conditions in order to avoid 

 bacterial activity. The fermenting mixtures obviously -cannot 



* Bayliss: " J. PhysioU," 1912, 44, Proceedings, ix, and 1913, 46, 236. 



