184 COLLOIDS IN BIOLOGY AND MEDICINE 



Even the colloidal state itself, i.e., great surface development, under 

 certain circumstances, may be responsible for work similar to that per- 

 formed by certain of the enzymes. For instance, G. BREDIG catalyzed 

 hydrogen peroxid by means of metal sols, particularly platinum sol, 

 which he prepared by electric pulverization; that is, he obtained a 

 result, the splitting off of oxygen, which in all appearances resembles 

 that brought about by catalase, a ferment which occurs in blood, in 

 milk, and in many plant and animal tissues. On this account G. 

 BREDIG called his metal sols "inorganic ferments," although with 

 enzymes (or ferments), they share other properties to which we shall 

 return. The action of enzymes is explained in part by their colloidal 

 nature. In the organism they act chiefly on colloid substances 

 (e.g., foods) with very extensively developed surfaces, so that under 

 certain circumstances enzymes may be merely mechanically adsorbed. 

 They consequently act upon the substrate in the greatest concentra- 

 tion. 



It was shown by numerous adsorption experiments with indiffer- 

 ent suspensions (charcoal, kaolin, cellulose) that enzymes have a 

 strong tendency to concentrate on surfaces. It is possible to remove 

 the rennin or pepsin (M. JACOBY*), and trypsin (G. BUCHNER and 

 KLATTE*) from solution by means of fibrin flakes or other coagulated 

 albumin, or diastase by means of starch (H. VAN LAER). The 

 reagents and sometimes also the products of the reaction are adsorbed 

 by the colloidal enzymes. If the former accumulate, in accordance 

 with recognized laws, the progress of the reaction is slowed. An 

 example is the breaking down of hydrogen peroxid by catalase. The 

 oxygen formed by the breaking down of H 2 O 2 into H 2 and O is ad- 

 sorbed by catalase and the reaction is slowed ( WAENTIG and STECHE) . 

 Some enzymes, especially pepsin and papagotin, according to ROHONGI, 

 give reversible precipitates in salt-free, neutral solutions of different 

 albumins on which they act. The inhibition of the action of an 

 enzyme by a suspension or a colloid may be removed again under 

 certain conditions by another indifferent colloid. If the activity of 

 rennet has been destroyed by charcoal or normal serum so that the 

 mixture no longer produces curdling of milk, the activity of the 

 rennet may be restored by the addition of saponin. Somewhat 

 different modifications are obtained by the addition of cholesterin 

 or by combinations of trypsin with charcoal, saponin or cholesterin 

 (JOHNSON, BLOM*). In this way, the numerous possibilities which 

 result from the interaction of enzyme and antienzyme (q.v.) rest on 

 a physical basis. 



The essential difference between an indigestible adsorbent and one 

 which is dissolved by the enzyme is that the combination, e.g., be- 



