154 PRINCIPLES OF SOIL MICROBIOLOGY 



1,500,000 of the first, 22,500,000 of the second, and 4,000,000 of the 

 third. Aeration of soil and the addition of organic matter bring about 

 the greatest numerical increase in the group of non-spore-forming bac- 

 teria in the soil. The above numbers as determined by the plate method 

 represent only a fraction of the actual abundance of these organisms in 

 the soil, since they live in zooglea-like masses imbedded in the soil col- 

 loids and cannot be readily separated into individual cells. 



Of the non-spore-forming bacteria and cocci, some are especially 

 abundant in the soil. The available information on this subject is very 

 meager due largely to the difficulty of studying some of the slow growing 

 organisms on artificial media. The Bad. fluorescens is especially abun- 

 dant, having been found in soils all over the world. The same is true of 

 certain cocci or very short rods. 



Severin 24 found rods to predominate in freshly plowed manured soil 

 as well as in manure itself; however, in two weeks cocci predominated 

 According to Houston, 25 Bad. vulgar e (Proteus vulgaris), Bad. prodigi- 

 osum and various Saicinae are less abundant in the soil than the 

 spore-forming bacteria, actinomyces, and the Bad. fluorescens. When 

 inoculated into soil, Bad. prodigiosum persisted only when the soil 

 was previously sterilized and kept moist; when the soil was air dried 

 or when the inoculation took place into non-sterile soil, the organism 

 was rapidly destroyed. The occurrence of brown fluorescent bacteria 

 in the soil was pointed out by Bazarewski. 26 Barthel 27 found in a 

 North Greenland soil Bad. fluorescens, Bad. caudatum, Bad. pundatum, 

 Bad. violaceum, Bad. ladis viscosum, Bad. umbilicatum, Bad. ochraceum 

 and Bad. zopfii. Among the cocci, Barthel found Tetracoccus and Sar- 

 cina flava. In addition to these organisms, various other bacteria, 

 like those forming a blue pigment, those accompanying the nitrogen- 

 fixing organisms, various spirilli, vibrios, and cocci have been reported 

 to be found in the soil by different investigators. Certain organisms, 

 like Bad. vulgare, Bad. colt and others, present abundantly in manure and 

 feces, are thus abundantly introduced into the soil and may survive 

 there for a long time, some of which, such as various proteolytic and 

 cellulose-decomposing bacteria, may even become active there. 



24 Severin, S. A. Die im Miste vorkommenden Bakterien und deren physi- 

 ologische Rolle bei der Zersetzung desselben. Centrbl. Bakt. II, 1: 100-104. 

 1895; Zhur. Opit. Agron. 1: 463-489. 1900. 



"Houston, 1898 (p. 14). 



26 Bazarewski, S. v. tlber zwei neue farbstoffbildenden Bakterien. Centrbl. 

 Bakt. II, 15: 1-7. 1905. 



27 Barthel, 1922 (p. 149). 



