THE PEOTIC SUBSTANCES 67 



SOURCE OP PECTASE. 



To obtain the enzyme, leaves of Syringa vulgaris were 

 pressed in a vice, and the resulting liquid was either em- 

 ployed directly, after removal of debris by the centrifuge, 

 or its pectase was precipitated by alcohol and redissolved 

 in distilled water. The fresh sap contained both calcium 

 salts and other electrolytes, whereas the precipitated 

 enzyme mixture was to a great extent free from both. 

 Attempts were made to correlate the activity of the sap 

 with the age of the leaf, but fluctuations from sample to 

 sample obscured the influence, if any, of this factor. 



ELECTRICAL CONDUCTIVITY or GELATINIZING PECTIN 

 SOLUTIONS. 



Since the electrical conductivity of a solution at con- 

 stant temperature depends both upon its concentration 

 of electrolytes and the viscosity of the medium, it was 

 thought that measurements of this character might throw 

 light upon the phenomena of gelatinization. For whereas 

 a liquid such as glycerol has a high viscosity both as regards 

 its time of flow through a capillary tube and its effect upon 

 electrolytes, another, such as a gelatin solution,* may have 

 an equal viscosity as measured by time of flow, but when 

 its effect upon electrolytes is the criterion the difference 

 between it and the pure solvent may be negligible. Thus, 

 leaving out of account possible changes in the chemical 

 character of the pectin leading to increase or decrease in 

 conductivity during gelatinization, it is clear that, if but 

 little change occurs in the resistance of the solution while 

 the pectase is acting on it, there can be no doubt that the 

 structure of the product is that of a jelly, a mesh work of 

 a colloid containing a colloidal liquid solution, rather than 

 * This, of course, is not a homogeneous solution. 



