198 THE LIVING ORGANISMS OF THE SOIL [chap. 



can only be replaced by others which are tolerant of 

 acid conditions. The presence of chalk, or any form 

 of carbonate of lime, by neutralising any acids as fast 

 as they are formed, promotes the destruction of organic 

 matter. Wollny has also shown that calcium humate 

 will oxidise much more rapidly than uncombined humic 

 acid placed under similar conditions. Portions of the 

 acid grass plots at Rothamsted have been limed, where- 

 upon the peaty surface accumulation rapidly disappears. 

 To the absence of carbonate of lime and mineral salts 

 generally, may be ascribed the tendency of humus to 

 accumulate and persist on the very light, sandy heaths, 

 where the soil is dry and hot in summer, and also well 

 aerated. It has already been indicated, in treating of 

 humus, that the various organic compounds of nitrogen 

 show very different susceptibility to the breaking-down 

 process which eventually renders the nitrogen available 

 for the crop amongst the most resistant substances 

 being the nucleo-proteins in the undigested portions 

 of food which form dung, and the humus residues from 

 poor, cropped-out land. As in all cases much of the 

 nitrogen of both soil and manure seems to pass into 

 obstinately persistent compounds yielding slowly, if at 

 all, to oxidation, and hence wasted to the farmer, an 

 attempt has been made to increase the preliminary 

 breaking down of nitrogen compounds in the soil 

 by the introduction of certain very active bacteria. 

 Stoklasa has shown that various organisms B. mega- 

 tkerium y B. fluoresced) etc. when seeded into soil 

 manured with bone-meal or similar materials, increase 

 both the nitrogen and the phosphoric acid obtained by 

 the plant. A pure cultivation of some such organism, 

 B. Ellenbachensis, was for a time sold commercially 

 under the name of alinit, and though the power of 

 fixing nitrogen was claimed for it, its chief action was 



