PROXIMATE PKINCIPLES. 
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 nutri- 
Uon^ and distinguishes living substances from dead matter. A 
stone does not receive nourishment, although it may increase 
by an external accumulation of matter. " Yegetable substances, 
analyzed by a cliemical process, have been found to contain 
carbon^ oxygen^ hydrogen^ and sometimes nitrogen^ svlpJiur^ 
silex^ the oxide of iron^ soda^ magnesia^ and cJialh.''^^ 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 
distinguished by the name of 'proximate priticiples. 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, hydrogen, and nitrogen are the most important of 
the ultimate elements of plants, and the constituent parts of their proximate prin- 
ciples. These principles may be divided into two classes. I. Those principles 
wliich are composed of carboti, 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 this 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 
wliich 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 is 
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 the genera Oxalis and Rwnex. Tartaric 
acid is obtained from the tamarind and cranberry ; this acid, combined with potash, 
forms what is commonly called cream 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 
\^;nzoin and Vanilla ; this is highly aromatic ; it is thought to give the agreeable 
odor common to balmsu Prussic 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, <fec. 
d. The 2d order includes gum, sugar, &c. The Gxmis. 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, such 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. All 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." t By sojne writers called Acacia arabica. 
140. Tlie plant, chemically considered — a. Proximate principles— Proximate principles divided vtia 
two elasse-s- -A. First class divided into three orders— c. First order— <Z. Second order— c. Third order. 
