1 84 BACTERIA AND SOIL FERTILITY 



returned to the soil. The quantity carried to a soil with ma- 

 nure may vary from a few per cent to one-half the total dry 

 weight, depending on the age, kind of manure, and litter used in 

 bedding the animals. Now, where the farmer burns straw and 

 other cellulose containing material on the soil, the phosphorus and 

 potassium would all be left in the ash. Most of the nitrogen and 

 all the cellulose would be lost. But when the straw is left to 

 decay, it serves as food for cellulose ferments and incidentally 

 changes the chemical and physical aspects of the soil. 



Early Observations. — That carbon passes through a definite 

 cycle from the solid organic tissues of plants to the gaseous form 

 of the atmosphere has been known for a long time, but it was 

 usually thought of as passing from the solid complexes to the 

 gaseous compounds through its direct combination with oxygen at 

 a high temperature. In fact, this was considered as being the 

 only method until Pasteur pointed out that there were other 

 means. He considered it as being brought about by molds. Later 

 Mitscherlich (1850) observed that when moist potatoes decay 

 the cell wall is dissolved and the starch gradually passes out. This 

 he considered due to the action of microorganisms, but nothing 

 was done to show that it was the work of any species until about 

 fifteen years later when Trecul isolated an organism which had 

 the power of decomposing young plant tissues and which was 

 stained blue by iodine. To this organism he gave the name 

 amylobacter The organism he claimed had the power of de- 

 composing cellulose with the formation of butyric acid, carbon 

 dioxid, and hydrogen. As all of his work was carried on with 

 plant tissues, however, it left a question as to whether the amylo- 

 bacter had actually decomposed cellulose or only some of the 

 nearly related compounds. 



Some of the earliest work done to determine the change through 

 which cellulose passes in soil was that of Hoppe-Seyler who com- 

 menced his experiments by collecting and analyzing the gases 

 given off from soils and swamps. These he found to consist 

 mainly of carbon dioxid and methane. Later he carried out 

 laboratory determinations by placing 25.773 §^* ^^ filter paper 



