PEOXIMATE PRINCIPLES. 115 



140. Before closing our view of the vegetable structure we 

 will by the aid of chemistry examine the elements which com- 

 pose it. The growth of vegetables, with the increase of their 

 weight, shows that they imbibe some external matter which is 

 incorporated into their own substance. This constitutes nictri- 

 tion^ and distinguishes living substances from dead matter. A 

 stone does not receive nourishment, although it may increase 

 by an external accumulation of matter. " Vegetable substances, 

 analyzed by a chemical process, have been found to contain 

 carhon^ oxygen^ hydrogen^ and sometimes nitrogen^ svlpliur^ 

 silex^ the oxide of iron^ soda^ magnesia^ and cJialky^' These, 

 by the agency of the root, stems, and leaves of the plant, are 

 derived from the earth,. air, and water. 



a. Proximate Principles. — Vegetation produces chemical combinations which are 

 6xsi\n^\\ii\\eilhj \\xe naxne oi proxiinate principles. Although the proximate prin- 

 ciples of plants are very numerous, but few of them are well known ; they are the 

 result of the action of the vital forces of plants, and are, therefore, important sub- 

 jects of investigation to those who pursue the study of physiological botany to any 

 great extent. Carbon, oxygen, liydrogen, and nitrogen are the most important of 

 the ultimate elements of plants, and the constituent jjarts of their proximate prin- 

 ciples. These principles may be divided into two classes. I. Those principles 

 which are composed of carbon, hydrogen, and oxygen, without any nitrogen. 

 II. Such as contain, besides the substances belonging to the other class, some nitro- 

 gen. There are few of tliis class, 



b. The FIRST CLASS of proximate principles is divided into three orders. 1st. Prin- 

 ciples which have more oxygen than sufficient to form water. 2d. Principles in 

 which oxygen and hydrogen exist in the exact proportion to form water. 3d. Prin- 

 ciples where hydrogen is in excess. 



c. The 1st order includes vegetable acids ; as, Acetic acid, or pure vinegar ; this ia 

 generally produced by fermentation from wine, cider, and some other hquids ; it is 

 also found in a pure state in Campeachy wood, and the sap of the elm. Malic acid 

 may be extracted from green apples and the barberry. Oxalic acid is found in 

 several species of sorrel belonging to tlie genera Oxalis and Pumex. 2'artaric 

 acid is obtained from the tamarind and cranberry ; this acid, combined with potash, 

 forms what is commonly called crearn of tartar. Citric acid is found in the lemon ; 

 it is mixed with malic acid in the gooseberry, cherry, and strawberry. Quinic acid 

 is obtained from the Peruvian bark {Cinchona). Gallic acid is obtained from the 

 oak and sumach ; it is highly astringent. Benzoic acid is found in the Laurus 

 benzoin and Vanilla; this is highly aromatic; it is thought to give tlie agreeable 

 odor common to balms. Pricssic acid gives out a strong odor like bitter almonds ; 

 it is an active poison ; it is obtained from peach-meats and blossoms, from bitter 

 almonds, (fee. 



d. Tlie 2d order includes gtim, sugar, &c. The Gums. Of these there are many 

 kinds ; they have neither taste nor smell ; dissolved in water, they form a mucilage 

 more or less thick. The principal gums are, Gum Arabic, which flows from the 

 plant Mimosa nilotica ;\ Common Gums,s.\\c\\ as issue from the peach-tree, the 

 cherry-tree, and many other plants. Sugar is a substance which dissolves in water, 

 and has a sweet taste' ; it is obtained from the sugar-cane, sugar-maple, from the 

 stalks of Indian corn, pumpkins, beets, and sweet apples. Ail vegetables which 

 have a sweet taste may be made to yield sugar. Starch is a general product of 

 vegetables ; it may be converted into sugar. 



* Mirbel, " Elemens de Botanique." f By some writers called Acacia arabica. 



140. The plant chemically considered— a. Proximate principles— Proximate principles divided into 

 iwo classes- -h. First class divided into three orders— c. First order— cf. Second order— e. Third order. 



