408 SCIENCE PROGRESS 



From what has been said above, it may be assumed that 

 ample earher evidence exists for the classifying of enzymes as 

 catalysts. The factors governing or influencing this catalytic 

 action will therefore be dealt with. 



One of the most important physical properties of enzymes is 

 their colloidal nature, which renders them insoluble in water 

 in the usual sense, but readily allows them to form fine sus- 

 pensions in what may be considered a very dilute solution of 

 themselves. 



Dispersion. — As colloids, therefore, enzymes have the great 

 colloidal characteristic, viz. the enormous development of 

 surface, and it will be seen that many of the properties of 

 enzymes and of factors influencing them depend on the ultimate 

 dispersity of the particles suspended. Important work was 

 done on this subject by Nelson and Griffin (1916) and will be 

 referred to later. 



The amount of dispersion of the particles may be seen with 

 the aid of the ultramicroscope, and by this means Casana 

 (191 3) found that the dispersion of trypsin particles was greater 

 when the temperature was raised and the activity of the enzymes 

 had increased. Similarly it has been found that the solubilities 

 and action of such enzymes are related to the dispersive powers 

 of the solvent. Thus glycerol, which has good dispersive power 

 over colloids, is frequently used to extract enzymes. 



De Jonge (191 7), following up the work of Terroine (19 10), 

 came to the conclusion that the action of bile depended not 

 only on the emulsification of insoluble fats, but that by lowering 

 surface tension, with consequent increase of dispersity, colloidal 

 aggregation of enzyme was prevented, or a greater surface 

 developed as a result of the production of disaggregation. 

 Further reference will be made to the work of this observer 

 under " Adjuvants." This conclusion was supported by Groll 

 (191 8) after his investigation of the retarding effects of metals 

 on enzyme action. He found that the retarding effect of NH4 

 was greater than that of K, which was greater than that of Na, 

 and so on, and considered the action to be similar to floccing 

 and other colloidal phenomena. This led him to the general 

 conclusion that very possibly the influence of all neutral salts 

 on enzyme action was due to the fact that the dispersity of the 

 enzyme was modified by the ion in the same way as other 

 colloids. The work of Albert and Alexandre Mary in the 

 same year, although unconfirmed, gives a striking instance of 

 a similar action in relation to an inorganic catalyst. They 

 found that colloidal silica can invert saccharose slightly, and 

 that its activity increases in proportion to the degree of dis- 

 persity. They arrived at an optimum temperature, and also 

 found absolute inactivation when coagulation was complete. 



