100 



Decomposition of Plant and Animal Residues 



7. Alkaloids and organic bases, including purine bases, pyridine, 

 and piperidine compounds. 



8. Proteins, polypeptides, amino acids, amines, and other ni- 

 trogenous compounds. 



9. Enzymes, hormones, vitamins, pigments, antibiotics, and other 

 important products of living systems, the exact chemical nature of 

 some of which still remains unknown. 



Fig. 48. 



Cellulose 



Influence of age upon the chemical composition of rye ijlants (from 

 Waksman and Tenney). 



10. Mineral constituents: phosphates, silicates, sulfates, carbonates, 

 chlorides, nitrates, and potassium, sodium, calcium, magnesium, and 

 other salts. 



It is almost impossible to make a complete quantitative analysis 

 of plant and animal materials, whereby all the chemical constituents 

 are accounted for. For most purposes, it is sufficient to account for 

 some of the more important groups of compounds, to obtain a 

 fairly good idea of the chemical composition of the materials which 

 undergo decomposition. Such an analysis need be only proximate 

 in nature. It may be supplemented by special determinations of 

 certain compoimds wliich are either characteristic of a given ma- 

 terial or essential for the understanding of a certain process. In a 

 proximate analysis, only those compounds which occur most abun- 

 dantly in the plant and the decomposition of which is best under- 



