I2O SOME PRACTICAL LESSONS FROM SOIL BACTERIOLOGY. 
method should always be tried. Soil from some locality where the 
legume grows luxuriantly should be imported and mixed with the 
field which is to be planted with the legume. But one should be 
careful that the inoculating soil does not bring troublesome weeds or 
plant diseases. In using either the earth inoculations or pure 
cultures, it must be borne in mind that if a soil is already well stocked 
with the tubercle bacteria, inoculations are not likely to do any good; 
but in soils where a new legume is to be grown or where the legume 
to be planted does not flourish, soil inoculation may be of decided 
advantage. 
Soil Inoculation with Manure. Manure is added to the soil 
primarily as a means of furnishing plant food; but it has become 
evident that the inoculation of the soil with the immense amount of 
bacteria in the manure is in itself of extreme value, sometimes, as in 
pasture soil, of more value than the actual food substances in the 
manure. The use of manure upon the soil must, therefore, be 
looked upon as one of the very useful methods of inoculating the 
soil with the bacteria needed to carry out the soil transformations. 
CONTROL AND STIMULATION OF SOIL BACTERIA. 
It has become more and more evident, as information has ac- 
cumulated, that a vigorous activity of the bacteria found in the soil 
is needed to carry out the various transformations of plant foods. 
These bacteria are commonly abundant enough; and sometimes 
they find the conditions so favorable that they grow rapidly, pro- 
ducing vigorous actions; but at other times the conditions in the 
soil are unfavorable, and they are held in check. What is chiefly 
needed, then, in the treatment of soil is, not the inoculation of more 
bacteria, but a modification of the soil conditions so as to favor the 
growth of those already there. While this is a complicated sub- 
ject and one that will require different treatment in different cases, 
a few general principles may be formulated. 
Acidity. Most bacteria, and practically all the useful bacteria, 
are very sensitive to the presence of acid, failing to grow at all in 
an acid medium. If the soil is but slightly acid, bacterial agencies 
