1911.] 



TJie Properties of Colloidal Systems. 



89 



calcium sulphate contained in the 2 c.c. of filtrate on the course of the 

 hydrolysis itself. Calcium salts are known to have a favouring effect on 

 many enzymes. This effect may, of course, be due to the increased adsorption 

 of enzyme by substrate in the digesting system itself. In the case of the 

 other adsorbents, the effect of the small amount of calcium salt in the enzyme 

 solution was overpowered by the opposite effect due to actual diminution of 

 the total amount of enzyme present. 



At the same time, experiments with sugar charcoal containing a minimum 

 of electrolytes indicate that the above explanation of the anomalous behaviour 

 of charcoal does not entirely account for the phenomena. It was found, in 

 fact, that, although the sugar charcoal did not give quite so marked a 

 difference as bone charcoal, yet it was in the same direction, and opposite to 

 the effects with other adsorbents. The particular sample used (Kahlbaum's) 

 was in an extremely fine powder, which could not be filtered off completely 

 from the suspensions in distilled water. After the action of calcium sulphate 

 it was aggregated to such a degree that filtration was easy.* The less 

 adsorption in presence of the salt may therefore possibly have been due to 

 the aggregation and consequent diminution of the active surface of the 

 adsorbent. An experiment was made in order to see whether this aggrega- 

 tion by calcium sulphate could be prevented by the presence of a stable 

 colloid, such as gelatin. 



In this experiment it was found, indeed, that the addition of gelatin in such 

 amount as to make a concentration of 05 per cent., which was too dilute to 

 gelatinise at room temperature, prevented the aggregation of charcoal by 

 calcium sulphate. But it also prevented the action of the calcium salt on 

 the adsorption of trypsin by charcoal, since the filtrate from the preparation 

 containing the gelatin contained more enzyme than that from the control 

 preparation without gelatin. This effect is, in fact, similar to that observed 

 when stable colloids are present in experiments on the adsorption of Congo 

 red by filter paper under the influence of neutral salts.f 



The results of the preceding section afford confirmatory evidence for the 

 hypothesis of adsorption compounds between caseinogen and trypsin, as well 

 as between trypsin and inert bodies. It will be seen that the behaviour of 

 both is the same with respect to salts. Of course, 1^he experiments afford no 

 evidence for or against subsequent chemical combination. 



* It was also deprived of its electric charge, as shown by the absence of any movement 

 in an electric field. 



t ' Biochem. Journ.,' 1906, vol. 1, p. 201. 



