^66 THE POPULAR SCIENCE MONTHLY. 



the alcoholic fermentation, even before maturity is passed. H. Gut- 

 zeit (Zeitscher Oest. Ap. Ver., 1875, p. 337; Pro. Am. Phar. Asso., 

 1876, p. 287) reports finding alcohol, or other simple compound of 

 ethyl, in the fruits of a number of plants. Some of the fruits were 

 not quite ripe, and none were overripe. De Luca ( Comptes He)idus, 

 lxxxiii., 512; Jour. Chem. Soc, 187G, ii., 649) reports obtaining prod- 

 ucts of the alcoholic and acetic fermentations from the fresh fruits, 

 leaves, and flowers, of several plants. In all these cases the quantities 

 of alcohol obtained were very minute. The investigator first above 

 named found methyl-alcohol, in some cases, with the ethyl-alcohol. 

 Pasteur states that the germs which excite alcoholic fermentation are 

 very abundant on the bunches of ripe grapes, where very rare in the 

 atmosphere. Also, that the fermentive germs are found on ripe straw- 

 berries, cherries, and currants, but not on the same fruits unripe. The 

 formation of methyl-alcohol, above referred to, is closely allied to the 

 formation of metliyl-salicylate or wintergreen-oil. A number of the 

 essential or volatile oils, with which plants and fruits are perfumed 

 and flavored, contain alcohol radicals in union as compound ethers. 

 It is probable, from every point of view, that the slight occurrence of 

 the vinous fermentation in fruits belongs to an important class of 

 chemical formations, by means of which a multitude of odor-giving 

 substances are scattered throughout vegetation. We shall inquire 

 more carefully into the fruit-flavor compounds and their formation 

 further on. 



2. The Pectous Substances. These are, in general terms, the 

 constituents of plant-jelly. As vegetable products, they correspond 

 to the varieties of gelatine obtained from animal tissues. Unlike 

 gelatine, however, they are non-nitrogenous. They are found in the 

 soft parts of plants generally, as in the tuber of the potato and the 

 root of the carrot; but it is in fruits that they have most impor- 

 tance for edible value. The immediate origin of the pectous sub- 

 stances is pretty well known, being due to a specific fermentation, a 

 prominent feature in fruit-ripening. The material from which all the 

 pectous substances proceed is the fermentable body called pectose, an 

 insoluble, tasteless substance, found abundantly in unripe fruits, also 

 to some extent in immature roots and tubers, and having no more 

 value for food than cellulose. Now, there is formed along with this 

 substance a " ferment," as it is called, a body which by contact in- 

 duces a specific fermentation a definite chemical change. Pectase is 

 the name of the ferment. Just as, in the germinating seed, starch, 

 by contact with diastase, suffers fermentation with production of 

 sugar, and as, in bruised and wetted mustard-seeds, sinigrin, by con- 

 tact with nvyrosin, splits up into pungent oil of mustard and sugar, 

 etc., so the crude pectose of green fruits, by contact of their pectase 

 at the time of ripening, changes to the edible plant-jellies or pectous 

 substances. Long boiling with water alone effects the same change. 



