TRANSFORMATION OF ORGANIC MATTER 693 



mation of acids similar to natural humic acid, of the formula (C 6 H 4 3 ) x . 

 These compounds may condense with amino acids to give "humus;" 65 

 the black coloration produced by Bac. mesentericus niger in nutrient 

 media containing a carbohydrate was found to be due to components of 

 the benzene series closely related to o- and p-dihydroxybenzenes which 

 apparently form condensation products with the amino acids. Similar 

 results were obtained for bacteria and fungi. 66 



3. "Humus" is formed from the polymerization of furfural, the latter 

 being produced when acids are acting upon carbohydrates. 67 A dark 

 colored substance containing 75.1 per cent carbon results on heating 

 furfural or oxy-methyl furfural with hydrochloric acid. 68 A similar 

 compound was demonstrated in rotting straw and in the soil, but 

 not in the decomposition of cellulose by bacteria. 69 These three theories 

 can account only for a very small amount of "humus" in the soil. It 

 must be kept in mind that very strong mineral acids are not found in 

 normal soils and amino acids are not liberated in a free state to any 

 considerable extent. Even the benzene ring compounds, which are not 

 present in great abundance in natural organic substances, are decom- 

 posed by certain soil microorganisms. 



4. The formation of "humus" from lignins. 70 Lignins are present 

 in amounts ranging from 10 to 40 per cent in natural organic matter. 71 

 While the constituent celluloses, pentosans, and proteins are decom- 

 posed by microorganisms, more or less rapidly, when natural organic 

 matter is added to the soil, the fats, waxes and lignins are acted upon 

 only very slowly, and gradually accumulate in the soil. 



5. The role of microorganisms, especially by synthesizing fresh cell 



65 Muschel, A. Zur Chemie der Schwarzfarbung kohlenhydrathaltiger Nahr- 

 boden durch den Bac. mesentericus var. niger. Biochem. Ztschr., 131: 570-590. 

 1922. 



68 Perrier, A. Recherches sur la fermentation de quelques composes de la 

 serie cyclique et sur la formation de la matiere noire de l'humus. Ann. Sci. 

 Agron (4), 2: 321-350. 1913. 



67 Roxas, M. L. The reaction between amino-acids and carbohydrates as a 

 probable cause of humin formation. Jour. Biol. Chem., 27: 71-93. 1916. 



68 Marcusson, J. Die Synthese der Humine und Huminsauren. Ber. deut. 

 Chem. Gesell., 54: 542-545. 1921. 



69 Beckley, V. A. The formation of humus. Jour. Agr. Sci., 11: 69-77. 1921. 



70 Fischer, F. Was lehrt die Chemie liber die Entstehung und die chemische 

 Struktur der Kohle. Die Naturwiss., 9: 958-965. 1921; Schrauth, W. tlber 

 die chemische Struktur der Kohle. Brennstoffchemie., 4: 161-164. 1923. 



71 Ritter, G. J. Distribution of lignin in wood. Jour. Ind. Engin. Chem., 

 17: 1194. 1925. 



