BACTERIA IN THE SOIL 167 



able, as suggested, that many of the species of common 

 saprophytes normally existent in the soil act as auxiliary 

 agents to denitrification and putrefaction. At present we 

 fear they are disregarded in equal measure, and for the same 

 reasons, as the common water bacteria. An excess of either, 

 in soil or water, is not of itself injurious as far as we know; 

 indeed, it is probably just the reverse. It is, however, fre- 

 quently an index of value as to the amount and sometimes 

 condition of the contained organic matter. The remarks 

 made when considering water bacteria apply here also, viz., 

 that an excess of saprophytes acts not only as index of in- 

 crease of organic matter, but as at first auxiliary, and then 

 detrimental, to pathogenic organisms. It will require ac- 

 curate knowledge of soil bacteria generally to be able to say 

 which saprophytic germs, if any, have no definite function 

 beyond their own existence. It may be doubted whether 

 the stern behests of nature permit of such organisms. How- 

 ever that may be, we may feel confident, though at present 

 there are many common bacteria in soil, as also in water, 

 the life object of which is not ascertained, that as knowledge 

 increases and becomes more accurate this special provisional 

 group will become gradually absorbed into other groups 

 having a part in the economy of nature, or in the production 

 of disease. At present the decomposition, denitrifying, 

 nitrifying, 1 and nitrogen-fixing organisms are the only sap- 

 rophytes which have been rescued from the oblivion of ages, 

 and brought more or less into daylight. It is but our lack 

 of knowledge which requires the present division of sap- 

 rophytes whose business and place in the world is unknown. 

 5. The Pathogenic Organisms found in Soil. In addition 

 to these saprophytes and the economic bacteria, there are, 

 as is now well known, some disease-producing bacteria find- 



1 It has already been pointed out that the nitrifying bacteria, though able to 

 live on organic matter, do not require such either for existence or for the per- 

 formance of their function. 



