PROXIMATE PRINCIPLES OF THE SECOND CLASS. 79 



CHAPTER III. 



PROXIMATE PRINCIPLES OF THE SECOND CLASS. 



THE proximate principles belonging to the second class are 

 divided into three principal groups, viz : starch, sugar, and oil. 

 They are distinguished, in the first place, by their organic origin. 

 Unlike the principles of the first class, they do not exist in 

 external nature, but are only found as ingredients of organized 

 bodies. They exist both in animals and in vegetables, though in 

 somewhat different proportions. All the substances belonging to 

 this class have a definite chemical composition ; and are further 

 distinguished by the fact that they are composed of oxygen, 

 hydrogen, and carbon alone, without nitrogen, whence they are 

 sometimes called the " non-nitrogenous" substances. 



1. STARCH (C 12 H, 10 ). The first of these substances seems to 

 form an exception to the general rule in a very important particu- 

 lar, viz., that it is not crystallizable. Still, since it so closely 

 resembles the rest in all its general properties, and since it is easily 

 convertible into sugar, which is itself crystallizable, it is naturally 

 included in the second class of proximate principles. Though not 

 crystallizable, furthermore, it still assumes a distinct form, by 

 which it differs from substances that are altogether amorphous. 



Starch occurs in some part or other of almost all the flowering 

 plants. It is very abundant in corn, wheat, rye, oats, and rice, in 

 the parenchyma of the potato, in peas and beans, and in most 

 vegetable substances used as food. It constitutes almost entirely 

 the different preparations known as sago, tapioca, arrowroot, &c., 

 which are nothing more than varieties of starch, extracted from 

 different species of plants. 



The following is a list showing the percentage of starch occurring 

 in different kinds of food : ' 



1 Pereira on Food and Diet, New York, 1843, p. 39. 



