304 VINEGAR, CIDER, AND FRUIT- WINES. 



fruits undergo during their development and perfection. The 

 results of these researches are briefly as follows : 



1. The quantity of water contained in the pulp of a fruit is con- 

 siderable ; it varies between 45 and 90 per cent. In many fruits 

 the content of water remains unchanged during the different 

 periods of ripening, but, as a rule, it is somewhat greater in the 

 commencement. 



2. Fruits of the same kind examined at the same season of the 

 year alwavs contain the same quantity of water ; the same holding 

 good as regards the various parts of the pulp of a fruit. 



3. The solid constituents in the pulp of fruits amount to be- 

 tween 10 and 25 per cent.; they consist of soluble substances, 

 which dissolved in the water form the juice of the fruits ; and of 

 insoluble bodies which compose the membranes of the cells. 



4. The quantity of soluble substances always increases with 

 increasing ripeness, while the weight of the insoluble decreases ; 

 hence it may be said the soluble substances contained in the juice 

 of a fruit are formed at the expense of the insoluble portion of 

 the pulp. The bodies which become soluble are starch, pectose, 

 and a gum-like substance capable of being converted into gum. 



On this modification of the solid portion of the pulp of a fruit 

 depend also the changes a fruit undergoes in regard to hard- 

 ness and transparency during ripening. 



According to the mode of action of the pectase and acids upon 

 the pectose, all ripe fruits contain pectine. 



5. Various acid fruits, such as plums, cherries etc., are fre- 

 quently observed to secrete a neutral juice which, in consequence 

 of the evaporation of the water, leaves a gum-like substance upon 

 the exterior of the fruit. This phenomenon throws some light 

 upon the separation of gum as it appears in many trees, and which, 

 when it occurs very abundantly, is an actual disease. 



In fruits becoming thus covered with gum a transparent, 

 neutral substance insoluble in water occurs stored in the cells of 

 the pulp. Under the influence of nitrogenous substances, which 

 act as a ferment, and perhaps also of acids, this gum-like substance 

 is modified and transformed into actual gum, which is then con- 

 verted into sugar in the interior of the pulp of the fruit ; an ex- 



