138 BACTERIA IN THE SOIL 



according to Professor Marshall Ward, in support of the hypothesis 

 that one symbiont may stimulate another by exciting some body 

 which acts as an exciting drug to the latter just as truly as certain 

 drugs act as stimulants to some cell or organ of a higher animal, and 

 probably in a fundamentally similar manner. 



Before we leave the subject of the economic bacteria present in 

 the soil, it may be well to refer briefly to the application of the new 

 knowledge to agriculture. Whilst many of the details of our know- 

 ledge concerning "the living earth" have not passed beyond the 

 experimental stage, it is not to be wondered at that the New Soil 

 Science has been received with some caution, and possibly in some 

 quarters even scepticism. This is neither surprising, nor, as regards 

 the details, altogether undesirable. A number of the cardinal 

 principles, however, are now obtaining very general acceptance 

 amongst practical agriculturists. Briefly, these may be stated as 

 follows. That a soil which has been sterilised, or is otherwise not 

 occupied by soil bacteria, is necessarily an unfertile soil ; that the 

 disintegration and oxidation of organic matter in the soil are the 

 result of bacterial life and work; that the sowing, growing, and 

 feeding of the desirable soil germs are of as much importance to the 

 agriculturist to-day as is the sowing of seeds, or the growing and 

 feeding by manuring of plants ; that the physical and chemical 

 conditions of soil favourable to these bacteria are of as much value 

 to the agriculturist as the requisite physical and chemical conditions 

 for the growth of the yeast cell are to the brewer ; and indeed that 

 one of the essential functions of manure in the soil is to provide 

 favourable pabulum and conditions for the operation of these soil 

 ferments. 



In the further elucidation of these principles various series of 

 experiments, in addition to those at Eothamsted (under Sir J. B. 

 Lawes and Sir J. H. Gilbert) and at Woburn (under Dr Voelcker), 

 have been designed and carried out. Of such a nature are the well- 

 known Dalmeny Experiments originated by Lord Eosebery some 

 years ago. The chemists engaged in this series were aware that 

 though large doses of caustic lime would kill outright certain of the 

 economic soil bacteria, annual or biennial dressings of mild lime 

 added to the culture media, that is the soil, would materially assist. 

 the process of nitrification. Five acres of land have been worked as 

 a miniature farm, each division being divided into sixteen plots. The 

 soil is of very uniform character, and is of the usual loamy kind met 

 with in the low grounds of the Lothians. Each plot has been 

 manured, or left unmanured as the case may be, on a regular system, 

 so that the residual values of the different manures, as well as the 

 yield of crop, may be accurately dealt with. The crops grown are 

 regularly analysed in order to determine the feeding value. Concern- 



