356 Scientific Proceedings, Royal Dublin Society . 



In view of the results obtained in Experiment VI it seems possible that 

 the calcium or other metallic ions act in a purely physical manner in causing 

 coagulation. In this experiment sap was extracted from the leaves, and the 

 enzymes precipitated by the addition of five times its volume of alcohol. The 

 precipitated enzymes were redissolved in water, and added to pectin solution, 

 from wliich dissolved calcium salts were absent. In tliis way any electrolytes, 

 including calcium salts, would have been almost completely removed. The 

 experiment, therefore, affords no evidence that tlie gel wliich is formed is 

 composed of calcium pectate. 



If the statement of Bertrand and Mallevre is correct, namely, that in the 

 absence of calcium salts a mixture of pectase and pectin remains indefinitely 

 liquid, then it would seem that gelification, as well as coagulation, is due to 

 a minute trace of electrolytes. As far as gelification is concerned, the action 

 of tlie electrolytes is possibly indirect, and it may be that their presence is 

 necessary in order to allow the enzyme to exert its activity. 



If tliis is tlie case, then possibly the events which take place during the 

 coagulation of pectin are somewhat as follows : — Under the action of pectase 

 some kind of pectic acid is produced from tlie pectin. If electrolytes are com- 

 pletely absent, the mixture remains liquid ; but if any ions are present, and 

 especially if they belong to one of the divalent metals such as calcium, partial 

 precipitation of the colloid takes place. At first tliese colloidal particles will 

 be free from one another, and while this is the case the viscosity will remain 

 almost constant, thus explaining the first portion of the curves. As the action 

 of the pectase proceeds, and more material is formed, whicli can be precipitated 

 by the electrolytes, a semi-solid reticulum is gradually built up with a 

 consequent rise in viscosity. As the reticulum becomes denser, the viscosity 

 will increase rapidly ; but if electrolytes are present in larger proportion, or 

 if they are allowed to act for a sufficiently long time, clumping together of 

 the particles of colloid forming the reticulum of the gel takes place, and a 

 suspension is formed with a consequent diminution in viscosity. A maximum 

 viscosity will be reached when the rate of gel-foriuution becomes insuSicient 

 to counterbalance the clumping effect. 



All this is merelj' a suggestion, and further experiments would be 

 necessary in order to obtain more definite information on the changes which 

 take place ; but as I am unable to proceed with this work at present, it seems 

 better to publish the results which have already been obtained. 



