The Soil. 
383 
The investigation of the soil has grown apace of recent 
years. The soil surveys which are in progress in America and 
on the Continent are tending to correlate the properties of 
soils with the results of analysis,' and to lead to the recognition 
of definite soil types agreeing in origin, composition, natural 
flora, and suitability for certain crops. 
The point of view of the soil chemist and physicist has 
also been greatly modified. The soil is no longer regarded 
as an inert medium which simply acts as a mechanical plant- 
producing machine, but as the site of continual chemical and 
physical ’ changes, such, for instance, as the preparation of 
available plant food salts and the movements of water among 
the soil particles. 
But it is perhaps in soil bacteriology that the greatest 
advances have taken place ; within the last twenty years the 
chief problems of nitrification have been solved, denitrification 
and its causes and results have been much studied, the 
fixation of free nitrogen by the root nodules of the leguminosse 
has been worked out, and much attention has been given to 
the role of many individual soil organisms, one of the most 
interesting of which is that which when fed on carbohydrate 
takes up and fixes atmospheric nitrogen. 
All these matters are dealt with in a revised and expanded 
chapter in Mr. Hall’s new edition, and this chapter is especially 
commended to those who propose to revolutionise agriculture 
by soil inoculation, a subject on which so many rash statements 
have appeared in the public press. Mr. Hall’s book has all 
the freshness and authority of one who writes with the 
intimate knowledge derived from personal research. It is well 
illustrated by plates and by graphic tables and curves. We 
hope Mr. Hall will deal similarly with other branches of 
agricultural learning. 
