HISTOUKWI. BAC'KC.Korxn 



9 



2. The Soil rrriixl {1900-1919) 



Just as tho first period was initiatod and 

 greatlj^ iuHiicMiced by tlie work of C.'ohn and 

 Harz, the second period may be said to have 

 been initiated by the work of W. H. lieijer- 

 inck, on the role of aetinoniycetes in soil 

 processes. It was soon followed by that of 

 TTiltner and Stormer, on th(> aetiiioniycete 

 population of the soil. While studies on the 

 pathogenicity and classification of aetino- 

 niycetes continued during this period, as in 

 the work of Sanfeli('(>, Wright, and many 

 others, ever-growing attention was being 

 paid to the saprophytic actinomycetes, their 

 physiology, and their role in nature, thus 

 resulting in the broadening of our under- 

 standing of actinomycetes as a large and im- 

 portant group of microorganisms. 



In 1900, Beijerinck published a paper on 

 the activities of an organism belonging to 

 the group of Siiprophytic actinomycetes, 

 designated as Streptothnx chromogena. This 

 organism belonged to the ^•ery large group 

 of actinomycetes now included in the genus 

 Streptomyces. Beijerinck attempted to throw 

 light upon its physiology and its role in soil 



transformations. lie pointed out that actino- 

 mycetes in general are ()inni\()n)us organ- 

 isms, capable of living in ;iii cnxironment 

 rich in organic matter as well as in a very 

 poor en\ironment. lOven distilled water and 

 an ordinary laboratory atmosj)here are suffi- 

 ci(Mit for the growth of some of these forms. 

 Beijerinck emphasized, however, that ac- 

 tinomycetes are unabk^ to carry out such 

 processes as the fixation of atmo.spheric ni- 

 trogen, an ability ascribed to them later, on 

 insufhcient grounds, by others. He also found 

 that actinomycetes produce, in glucose me- 

 dia, traces of acid, probably lactic, and that 

 they are able to reduce nitrate to nitrite. It 

 was suggested that, under certain conditions, 

 the last process may lead to losses of nitro- 

 gen through the interaction of nitrites with 

 ammonium compoimds. 



Beijerinck believed that the black pigment 

 produced by certain actinomycetes on pro- 

 tein media might function as an oxidizing 

 agent. This led him to postulate the signifi- 

 cance of these organisms in natural proc- 

 esses. Actinomycetes were found to occur 

 alnuidantly in the soil to considerable depths, 



Figure 6. (Irowth of actinomvcetes in soil, us shown bv direct exniuination. 



