432 PRINCIPLES OF SOIL MICROBIOLOGY 



is then washed with (I) dilute (1 per cent) hydrochloric acid, (2) distilled water, 

 (3) dilute (2 per cent) KOH solution, (4) distilled water, (5) dilute HC1 solution, 

 (6) distilled water, (7) alcohol, and finally (8) ether. The cellulose is then 

 dried at 100° to 110° to constant weight, burnt off and the crucible is reweighed. 

 The difference obtained gives the amount of cellulose in 10 grams of soil. 



Soils rich in organic matter (so-called "humus soils") have to be 

 treated first with 10 per cent CaO, so as to neutralize the humus sub- 

 stances, which would prevent the solution of the cellulose, 15 or extracted 

 with 2 per cent solution of sodium hydroxide, then washed with water, 

 dilute acetic acid and water. To determine cellulose in straw, wood or 

 other natural products added to the soil, the latter is first treated with 

 sodium acid sulfite, and then extracted with Schweitzer's reagent; 16 

 the natural plant material may also be extracted with 2 per cent sodium 

 hydroxide solution, at 15 pounds pressure, for 30 to 60 minutes, then 

 washed and boiled with 2 per cent solution of sulfuric acid and washed, 

 and only then extracted with Schweitzer's reagent; the precipitation 

 of the cellulose, filtering, washing and igniting is carried out as in the 

 case of pure cellulose. 



Mechanism of decomposition of cellulose by microorganisms. Mits- 

 cherlich 17 was the first (1850) to attribute the fermentation of cellulose 

 to the activities of microorganisms. Popoff ls demonstrated in 1875 

 the connection between cellulose decomposition and methane formation; 

 in the anaerobic decomposition of organic matter, the C0 2 :CH 4 ratio 

 was found to be 1:1. Tappeiner 19 established conclusively that micro- 

 organisms are concerned in the decomposition of cellulose. 



In studying the bacterial changes which take place normally in the intestinal 

 canal, Tappeiner introduced finely divided cotton or paper into flasks containing 

 a 1 per cent neutral solution of beef extract. The flasks and contents were 

 sterilized and then inoculated with small quantities of pancreatic juice and 

 incubated at 35°C. They were so arranged that the gases could be collected 

 and analyzed. The resulting product consisted of acetic acid, isobutyric acid, 



15 Dmochowski, R., and Tollens, B. tlber eine neue Methode der quanti- 

 tativen Zellulosebestimmung. Jour. Landw., 58: 1-20. 1910. 

 16 Bengtsson, 1925 (p. 680). 



17 Mitscherlich, E. tlber die Zusammensetzung der Wand der Pflanzenzelle. 

 Ber. Bekanntmach. Verhandl. Konigl. Preuss. Akad. Wissensch. Berlin, 1850, 

 102-110. 



18 Popoff, L. tlber die Sumpfgasgarung. Arch. Ges. Physiol., 10: 113-146. 

 1875. 



19 Tappeiner, H. Uber Celluloseverdauung. Ber. deut. chem. Gesell., 15: 

 999-1002. 1882; Ztschr. Biol., 20: 52-134. 1884. 



