MICHIGAN ACADEMY OF SCIENCE. 
51 
organic matter is later an air space, a channel for ventilation. The 
oxidation of soluble ferrous salts to insoluble ferric salts is apt to 
change the structure of soils, and so does the solution of insoluble phos- 
phates and carbonates by acids formed by microorganisms. There must 
be considered further the mycelial growth of molds, and possibly the 
formation of slime by bacteria. The experiences with sand filters indi- 
cate the probability of such influences. 
These are some of the great problems which seem to our laboratory 
the must urgent problems of the soil bacteriology of today. There are 
many other problems waiting for solution, and they may seem more 
important to other laboratories. 
The solution of such problems depends largely upon the develop- 
ment of the technique. The interest of the microbiologist concentrates 
in the products of microbial metabolism, and the success of determining 
accurately the character and quantity of the products of any decom- 
position depends upon the accuracy of the chemical analysis. The 
difficulty of analyzing the many compounds in soil has already been 
pointed out by the chemist's paper. Any improvement in the accuracy 
of chemical analysis will be of benefit to the bacteriologist. The new 
method of determining very small amounts of nitrogen which has been 
worked out in recent years by Mitsclierlich will no doubt open a new 
field to soil bacteriology. The method of determining amino-nitrogen in 
soils which has been worked out by Mr. Robinson, of the chemical depart- 
ment of our experiment station, will be of great value in the bacter- 
iological studies of the decomposition of humus and peat. 
But it is not only the chemical technique that limits the study of 
soil bacteriology. The main difficulty lies in the nature of the ma- 
terial we work with, namely the living organisms. While the chemist 
and physicist have a constant matter with which to work, the bacter- 
iologist deals with organisms that may multiply, or die, or lie dormant, 
that are influenced by slight changes of temperature, of moisture, of 
aeration. The variation of organisms under apparently equal condi- 
tions causes frequently a greater discrepancy of results than the prob- 
able error of chemical analysis. How difficult it is to avoid mistakes 
is seen in the different growth in soil and solution which was not con- 
sidered at all important for more than ten years. The problems of soil 
bacteriology are different from those of dairy bacteriology, and the 
methods used in the latter cannot be applied directly to the former. 
Soil problems require, above all, a careful consideration of soils as 
a medium for microbial development. The field is too new to permit 
bold, haphazard experiments. The conquest of such new land often 
necessitates a retreat on the whole line unless each step is guarded by 
reliable troops. This had not been the case in soil bacteriology, and 
the retreat was a hard lesson. Slowly, step by step, we must investi- 
gate the character of soils in relation to microbial growth, we must 
study the mutual relations of the various organisms, and since all 
bacteriological work is based upon the physiology of microorganisms, 
great efforts should be made to amplify our knowledge of the physiology 
of these smallest organisms. The solution of soil problems requires 
a strictly scientific study of all factors involved. Without such scien- 
tific basis, it may be possible after many mistakes to establish a few 
isolated facts but never a science of soil bacteriology. 
East Lansing, Mich., April, 1911. 
