32 



THE ACTINOMYCETES, Vol. I 



Table 4 



Numbers of bacteria and actinomycetes in various 



soils, as determined by the agar plate method 



(Waksman and Curtis) 



lated from the soil a special acidophilic 

 organism. The soil reaction had a marked in- 

 fluence upon the numbers of actinomycetes, 

 although there was no direct correlation be- 

 tween numbers and reaction. He suggested 

 that the low numbers in strongly acid peat 

 soils may be due largely to the poor aeration 

 prevailing in such soils. The addition of lime 

 brought enormous increases in the numbers 

 of actinomycetes. In a study of 56 Danish 

 soils, Jensen reported that the numbers var- 

 ied from none to about 13 millions per 

 gram, their percentage of the total micro- 

 flora developing on the plates being to 73.3 

 per cent. In Australian soils, he (1934) found 

 the numbers of actinomycetes to vary from 

 10 to 50 per cent of the total microflora. 



Using a starch medium with traces of ni- 

 trogen and certain minerals, Rao and Sub- 

 rahmanyan reported the presence in Indian 

 soils of 40,000 to 3,340,000 actinomycetes 

 per gram, as shown in Table 5. In a study 

 of the abundance of actinomycetes in heavy 

 loam Rothamsted soils, Singh observed a 

 broad relation between numbers of these 

 organisms and soil fertility: the heavilj^ ma- 

 nured soils gave the highest numbers and 

 the unmanured the lowest. 



Under certain exceptional conditions ac- 

 tinomycetes may make up the predominant 

 part of the soil microbiological population. 

 This was reported, for example, by Johns- 

 tone for the soils in the Bikini and Rongelap 

 Islands in the Pacific. The organic matter 

 content of the Bikini soil varied from 1.2 

 per cent at the surface to 0.56 per cent at a 

 depth of 6 inches, and the pH from 8.7 to 

 9.2. The total numbers of actinomycetes 

 were low, varying from 10,000 per gram at 

 the surface to 20,000 in the upper 6-inch 

 layer. The corresponding nimibers of bac- 

 teria were even lower, or about 1,000 to 

 2,000. The Rongelap soil was less alkaline 

 (pll 8.0 to 8.4) and contained much larger 

 numbers of actinomycetes, ranging from 



