178 JAMES M. SHERMAN 



from very serious consideration. A study of the methods he 

 used indicates, however, that the difference found in the soils 

 with and without protozoa might have been due to a difference 

 ill the complexity of the two flora, as was the case in the experi- 

 ments reported in Part IV (see Table XI) of this paper. In 

 fact, his manner of attack was very similar; sterilized soils were 

 employed as a substratum, and inoculations were then made 

 into these soils of cultures containing protozoa and free of pro- 

 tozoa. "One flask was inoculated with bacteria plus protozoa 

 from a culture of protozoa from soil, the other received as nearly 

 as possible an equal inoculation from the same culture of bac- 

 teria alone." It is not clear from this statement how he obtained 

 the bacterial culture free from protozoa, but it is very certain 

 that a protozoa-free culture could not be obtained which would 

 contain as complex a bacterial flora as did the original culture 

 fi-om which it was derived. As was previously pointed out, a 

 difference in the complexity of the bacterial flora in different 

 soils may cause a great disparity in the counts obtained by the 

 plate culture method. This fact was apparently not recognized 

 by Cunningham as he concluded that "the reduction in bac- 

 terial numbers in the soils inoculated with protozoa is very 

 marked and lies well outside the limits of experimental error." 

 A review of the data in Part IV of this paper will show, on the 

 contrary, that his results may fall well within the limits of ex- 

 perimental error. 



It is believed that the conclusions drawn from the work herein 

 reported will hold in general for the cultivated soils i]i this 

 country, but it is not desired to make too broad an application 

 of them. Many of the "sick" soils which have been studied 

 at the Rothamsted Experimental Station are very different from 

 the ordinary American soil. Martin and Lewin (1914) describe 

 a sick cucumber bed which was made up of one part of light 

 pasture soil, one part of heavy pasture soil and two parts of 

 horse manure, and had an optimum moisture content of 62 per 

 cent. The assumption that the biological conditions in such 

 a soil are the same as in the average soils of the United States 

 (which contain about 2 per cent organic matter and the optimum 



