Page:Popular Science Monthly Volume 12.djvu/484

468 be mentioned that Fresenius found widely-different quantities in the different varieties of the same fruit, and the average here drawn from the varieties of each fruit would greatly vary from an average obtained from other varieties of the same. The percentage in the fresh fruit is first given, and then percentage of solids, or strictly dry fruit, as obtained by calculation from the percentage of water:

As food-materials, the pectous substances seem to be wellnigh indispensable to the health of man. They are not very nutritious; it is not known that they are fully digested into material which can be appropriated; and, being non-nitrogenous, they could scarcely yield tissue-building matter. What service they perform is not clearly understood. They may supply liquids important in digestion or assimilation. We obtain them in acidulous fruits, and in starchy tubers, and it is not clear how much of the value of each of these sorts of food is due to their pectous constituents; but, when all food containing pectine is cut off, the scurvy is liable to ensue, and then any food supplying pectine will serve as a remedy. At the same time it is found that pectous food is needed only in small quantities; large proportions proving not only innutritious but injurious, causing derangements of digestion and excretion.

3. —The principal fruit-acids, not astringent, are the following, given in the order of their importance:

Malic acid: Very widely distributed; predominating in apples, pears, cherries, gooseberries, strawberries, raspberries, and mountain-ash berries. Not extracted for use.

Citric acid: Found in lemons, oranges, tomatoes, currants, gooseberries, raspberries, strawberries, and a large number of other fruits, generally with malic and tartaric acids. Obtained from lemons for use.

Tartaric acid: Also widely distributed in most fruits not forming the chief acid, but constituting the acid of the grape. Manufactured from the deposit of fermenting grape juice; used in baking-powders and in its salts, cream-of-tartar, and Rochelle salt.

Oxalic acid is sometimes found in small proportions in a few fruits. Reports vary as to its existence in the tomato.