106 PLANT COMPOUNDS 



acids, which are intermediate compounds formed in the 

 synthesis or hydrolysis of proteins. Third, proteins which 

 are the chief nitrogenous compounds in plants and are neces- 

 sary constituents of every living cell, whether plant or animal. 

 They are very complex, and are of various properties, 

 though generally colloidal in character. Fourth, alkaloids 

 which are nitrogenous bases of powerful physiological effect 

 on animals. 



The organic acids and their salts, besides those mentioned 

 before as constituents of fixed oils, volatile oils, and resins, 

 are noticeable in fruits for their acid taste. Tannic acid 

 is an exception. It is the chief constituent of tannin which 

 is a complex substance found in various plants, and used 

 for tanning hides and in dyeing. 



REFERENCES 



Allen. Commercial Organic Analysis, 4th ed., vols, i, ii, iii, iv, v, and vi. 



Browne. Handbook of Sugar Analysis. 



Cross and Bevan. Cellulose. 



Haas and Hill. The Chemistry of Plant Products. 



Parry. The Chemistry of Essential Oils. 



Rogers and Aubert. Industrial Chemistry, Chapters 25, 27, 29-33, 39. 



Thorp. Outlines of Industrial Chemistry, pp. 317-395, 521-532. 



