CHAPTBE III. 



HYDROCARBONACEOUS PROXIMATE PRINCIPLES. 



THE proximate principles belonging to this class are distinguished 

 from the preceding by their organic origin. They appear as products 

 of the nutritive actions of organized beings, and are not introduced 

 ready formed from the inorganic world. They exist both in vegetables 

 and in animals. In the former they are produced entirely as new com- 

 binations, under the influence of the vegetative process ; and even in 

 animals, which feed upon vegetables or upon other animals, they are so 

 modified by digestion and assimilation that they present themselves, as 

 final constituents of the body, under new and specific forms. They all 

 consist of carbon, hydrogen, and oxygen, of which carbon is present by 

 weight in especially large proportion, forming from 44 to 84 per cent, 

 of the entire substance. Owing to the absence of nitrogen, which is an 

 important element in organic substances of the following class, they are 

 sometimes known as the "non-nitrogenous" proximate principles. They 

 are naturally divided into two principal groups, namely: the carbo- 

 hydrates, or substances containing carbon, together with hydrogen and 

 oxygen in the proportions to form water ; and the fatty matters, in 

 which the proportions of carbon and hydrogen are both increased, while 

 that of oxygen is considerably diminished. The group of the carbo- 

 hydrates includes starch, glycogen, and sugar. 



I. Starch, C 6 H 10 5 . 



Starch is most abundantly diffused throughout the vegetable kingdom, 

 and exists, for at least a certain period of vegetative life, in every plant 

 which has yet been examined for it. It occurs especially in seeds, in 

 the cot3'ledons of the young plant, in roots, tubers, and bulbs, in the 

 pith of stems, and sometimes in the bark. 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, arrow- 

 root, and maizena, which are nothing more than varieties of starch, 

 extracted from different species of plants. 



The following list, compiled mainly from the tables of Payen, 1 shows 

 the percentage of starch occurring in various kinds of food : 



1 Substances Alimentaires. Paris, 1865. 



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