SUBSTANCES PRODUCED BY PLANTS. 59^ 



important influence on their value for food. Tiie fatty mat- 

 ters in plants are usually accumulated in the seeds, though 

 found in greater or less quantity in all their parts. In the 

 linseed and other seeds which contam them in large amount, 

 the oil is separated for commercial purposes by the pressure 

 of powerful machinery ; — the mass or cake which is left is 

 not entirely free from oil, and also contains other valuable 

 substances of the seeds, and is at present in great demand 

 for feeding cattle. Frequently, however, the fatty matters 

 exist in so minute quantities, or are retained with so much 

 force, in the cells of plants, that they cannot be abstracted by 

 simple pressure; but the chemist can remove and ascertain 

 their quantity by boiling the bruised seed in ether, in which 

 they readily dissolve. The solution, when exposed to the air, 

 allows the ether to evaporate while the oil remains behind.* 

 78. When the gluten procured by treating wheat flour as 

 described (74) is boiled in ether, we procure from it a fatty oil, 

 which is not very different in composition from the fat which 

 lubricates the machinery of the human body. A hundred 

 pounds of wheat yields about two pounds of this oil. The fatty 

 matters resemble starch and sugar in containing no nitrogen, 

 being formed from carbon, hydrogen, and oxygen only ; they 



* Composition of the cake of linseed, and of the cake of the seed of 



