Chapter VIII ^ ns — Distribution 



Methods of study.— Four methods can be used for determining the 

 presence and abundance of actinomycetes in the soil: I. the direct micro- 

 scopic method of stained soil; 2. the direct microscopic examination of 

 undisturbed or unstained soils; 3. the contact slide method; and 4. the 

 plate dilution culture method. Each of these methods has certain dis- 

 tinct advantages and limitations. 



Conn (77) was able to demonstrate, by the direct staining of the 

 soil, that the actinomyces mycelium is present abundantly in the soil, 

 especially in soils rich in organic matter. This method does not permit 

 the differentiation between actinomyces spores and certain bacteria. 

 Since the mycelium is not uniformly distributed in the soil, the method 

 does not permit an accurate quantitative evaluation of the abundance 

 of the organism. Furthermore, recognition of individual forms is often 

 limited, since in the process of staining, the mycelium is usually broken 

 up, and both mycelium and spores of various forms will appear similar. 

 The method may, therefore, be limited to the recognition of certain 

 broad groups rather than of specifiic types. 



Direct examination of undisturbed natural soils presents certain 

 marked advantages, since it gives a picture both of the relative abun- 

 dance of this group of organisms in the soil and its distribution through 

 the soil mass. Kubiena and Renn (245) used a vertically illuminated 

 microscope. Actinomycetes were found growing in the soil spaces open- 

 ing to the surface. Aerial tufts of hyphae in the form of more or less 

 compact colonies with long twisted strands were found to bridge the 

 gulfs between the soil crumbs. When the soil is enriched with organic 

 materials, such as proteins and lignins, the growth of actinomycetes is 

 greatly stimulated. 



The contact slide method offers certain advantages over the direct 

 staining method. It permits development of specific organisms upon 

 the slide, and even formation of fruiting bodies, thus making possible 

 the differentiation and recognition of certain broad groups. One is also 

 able to determine by means of this method, not only the gross effects 

 of additions of organic matter and lime to the soil, but also the response 

 in the development of actinomycetes to different types of fertilization 

 and cropping. The relation between pathogenic and saprophytic forms 

 to the root systems of plants can also be studied by the use of the con- 

 tact slide method. Cholodny (68) demonstrated, for example, that the 

 direct microscopic method gives a rather inaccurate picture of the abun- 

 dance of actinomycetes, as compared to the contact slide method. The 

 latter has, however, a marked disadvantage, since it gives no idea of the 

 relative abundance of actinomvcetes in undisturbed soil. 



By the use of the contact slide method, Waksman, Umbreit, and 

 Cordon (487) were able to demonstrate that, in composts kept at dif- 

 ferent temperatures, the fungi and the bacteria were the first groups of 

 microorganisms to develop at 50° to 65 °C.; however, these organisms 



