1 66 Fruits and Fruit- Trees. 



for the first time in Pliny. In Greek it took the shape 

 of kitros and kitrea, but not until after the classical 

 period.* 



The great value to mankind of these admirable fruits 

 consists in the abundance of citric acid which they 

 contain. Vegetable acids are invaluable, not to say indis- 

 pensable, adjuncts to human food. Nearly every fruit 

 eaten by man, and most of the parts of vegetables which 

 are eaten whole, contain more or less of some vegetable 

 acid. When such acids do not exist in food, recourse is 

 instinctively made to vinegar, acetic acid, produced by the 

 decomposition of various vegetable substances, and which 

 supplies the needful quantity. Of all the vegetable acids 

 known, the citric appears to be the most valuable and 

 efficacious. It exists in a considerable variety of fruits 

 and vegetables, but nowhere so remarkably as in the 

 fruits before us, the lemon and the lime in particular. 

 The exact mode of action of this acid is one of the 

 problems. So far as understood, it would seem to check 

 those unhealthy conditions of the system which culminate 

 in the disorder called scurvy, in bygone days so terrible 

 a scourge to sailors. Not that citric acid is the only anti- 

 scorbutic, either as a preservative or a curative. Large 

 and striking experience has proved, nevertheless, that 



* The Romans gave the name of citrus also to an extremely 

 celebrated kind of aromatic wood, furnished by the Callitris 

 quadrivalvis of Barbary, the same as the " thyine-wood" of the 

 Apocalypse, xviii. 12. Allusions to this wood are frequent in their 

 literature, and of course must be carefully distinguished from those 

 made to the fruit. 



