LESSON 26.] AND PRODUCING THE FOOD OF ANIMALS. 165 



475. But starch, sugar, and the like, do not make any part of the 

 flesh or fabric of animals. And that for the obvious reason, that they 

 consist of only the three elements carbon, hydrogen, and oxygen; 

 whereas the flesh of animals has nitrogen as well as these three ele- 

 ments in its composition. The materials of the animal body, cllled 

 Fihrine in the flesh or muscles. Gelatine in the sinews and bones, 

 Caseine in the curd of milk, &c., are all forms of one and the same 

 substance, composed of carbon, hydrogen, oxygen, and nitrogen. As 

 nitrogen is a large constituent of the atmosphere, and animals are 

 taking it into their lungs with every breath they draw, we might 

 suppose that they take this element of their frame directly from the 

 air. But they do not. Even this is furnished by vegetables, and 

 animals receive it ready-made in their food. And this brings us to 

 consider still another and most important vegetable product, of » 

 different class from the rest (omitted till now, for the sake of greater 

 simplicity) ; namely, what is called 



476. Proteine. This name has been given to it by chemists, be- 

 cause it occurs under such a protean variety of forms. The Gluten 

 of wheat and the Legumine of beans and other leguminous plants 

 may be taken to represent it. It occurs in all plants, at least in 

 young and growing parts. It does not make any portion of their 

 tissue, but is contained in all living cells, as a thin jelly, mingled 

 with the sap or juice, or as a delicate mucilaginous lining. In fact, 

 it is formed earlier than the cell-wall itself, and the latter is moulded 

 on it, as it were ; so it is also called Protoplasm. It disappears from 

 common cells as they grow old, being transferred onward to new or 

 forming parts, where it plays a very active part in growth. Mixed 

 with starch, &c., it is accumulated in considerable quantity in wheat, 

 beans, and ^ other grains and seeds, especially those which are most 

 nutritious as food. It is the proteine which makes them so nutritious. 

 Taken by animals as food, it forms their flesh and sinews, and the 

 animal part of their bones, without much change ; for it has the same 

 composition, — is just the same thing, indeed, in some slightly different 

 forms. To produce it, the plant employs, in addition to the carbonic 

 acid and water already mentioned as its general food, some ammo- 

 nia ; which is a compound of hydrogen and nitrogen. Ammonia 

 (which is the same thing as hartshorn) is constantly escaping 

 into the air in small quantities from all decomposing vegetable 

 and animal substances. Besides, it is produced in every thunder- 

 storm. Every flash of lightning causes some to be made (in the 



