20 AGRICULTURE. [CH. 



under certain circumstances of passing from one form 

 to another. It is worthy of note that although the 

 quantity of carbon varies slightly, the weight of oxygen 

 in each is exactly eight times the weight of the 

 hydrogen. Oil is found in large quantities in the 

 seeds of some of our cultivated plants such as 

 linseed, hemp, and cotton seed ; in smaller quantities 

 it is found in the grain of wheat, barley, oats, and 

 other varieties of corn. 



34. The three nitrogenous bodies are exceedingly 

 similar to one another in composition. It has been 

 already stated, that they not only contain carbon, 

 hydrogen, and oxygen, as did the several bodies of 

 the other group ; but they also contain nitrogen, 

 and because they contain nitrogen, they are called 

 nitrogenous. They are also called albuminoids, 

 after the name of their leading representative, albu- 

 men. This substance occurs nearly pure in the 

 white of the egg. It exists also in the juices of plants, 

 especially in corn and " roots." The gluten which 

 is separated from the flour of wheat in the manner 

 described (33), is largely composed of fibrin, an 

 albuminoid which occurs in blood, from which it is 

 readily separated by gently beating the fresh blood 

 with a few twigs. Little threads or fibres will soon 

 attach themselves to the sticks, and these will consist 

 of the fibrin of the blood. We shall hereafter see that 

 fibrin, or gluten, is an ingredient which largely deter- 

 mines the value of food. Casein occurs mixed with 

 fats in the curd of milk; it is also found in peas, 

 beans, &c., in which case it is sometimes called 

 legumin. 



35. We may now proceed to notice briefly the 

 sources from which plants obtain those substances 

 which we find them to contain. It is not difficult to 

 see that the inorganic matter is obtained from the soil, 

 because there is no other source from which these 

 materials can be obtained. It is also well known that 



