RIPENING OF FRUITS. 301 



Metapectine is soluble in water, non-crystallizable, and, like 

 pectine and parapectine, insoluble in alcohol, which precipitates 

 it from its solutions in the form of a jelly. On being brought 

 into contact with bases it is also transformed into pectic acid. It 

 differs from pectine and parapectine in that the solution is pre- 

 cipitated by barium chloride. 



Pectase, the peculiar ferment previously referred to, is similar 

 in its mode of action to diastase and emulsin. It can be obtained 

 by precipitating the juice of young carrots with alcohol, whereby 

 the pectose, which was at first soluble in water, becomes insoluble, 

 without, however, losing its effect upon the pectous substances. 



By adding pectase to a solution of pectine, the latter is imme- 

 diately converted into a jelly-like body, insoluble in water. This 

 phenomenon is the pectous fermentation, which may be compared 

 with lactic acid fermentation. It is not accompanied by an evo- 

 lution of gas, and may take place with the air excluded, a tem- 

 perature of 86 F. being most favorable for its progress. 



Pectase is an amorphous substance ; by allowing it to stand in 

 contact with water for a few days, it decomposes, becomes cov- 

 ered with mold-formations, and loses its action as a ferment, the 

 latter being also destroyed by continued boiling. In the vege- 

 table organism it occurs in a soluble as well as insoluble state. 



Roots such as carrots, beets, etc. contain soluble pectase, and 

 their juice added to a fluid containing pectine in solution imme- 

 diately induces pectous fermentation, while the juice of apples 

 and other acid fruits produces no effect upon pectine, the latter 

 being present in them in the modified insoluble form and accom- 

 panying the insoluble portion of the pulp. On adding the pulp 

 of unripe apples to a pectine solution it gelatinizes in a short 

 time in consequence of the formation of pectosic and pectine 

 acids. 



Pectosic acid is the result of the first effect of the pectase upon 

 pectine ; it is, however, also formed by bringing dilute solutions of 

 potash, soda, ammonia, or alkaline carbonates in contact with 

 pectine. In all these cases salts are formed which, when treated 

 with acids, yield pectosic acid. The latter is jelly-like and dissolves 

 with difficulty in water ; in the presence of acids it is entirely 



