4 68 



THE POPULAR SCIENCE MONTHLY. 



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 ob- 

 tained 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 quan- 

 tities ; large proportions proving not only innutritious but injurious^ 

 causing derangements of digestion and excretion. 



3. Acids. The principal fruit-acids, not astringent, are the follow- 

 ing, given in the order of their importance : 



Malic acid : Very widely distributed ; predominating in apples, pears, cher- 

 ries, 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 -tar- 

 tar, and Eochelle salt. 



Oxalic acid is sometimes found in small proportions in a few 

 fruits. Reports vary as to its existence in the tomato. 



