Soil Changes Produced By Micro-organisms. 
ii 
formic, and propionic. The first three of these are met with fre¬ 
quently around the farm, and when the place of their occurrence is 
mentioned, they will be recalled readily. Butyric acid gives the 
peculiar, rancid odor to butter and limberger cheese, and the bit¬ 
ter flavor to milk; lactic acid is the common acid of sour milk; the 
characteristic and pleasant acidity of cider vinegar is due to acetic 
acid. When such acids are set free in the soil, they act upon the 
mineral constituents and bring into solution certain compounds 
which are essential to plant growth. The acids are not apt to 
become very abundant in a well-drained and aerated soil, espe¬ 
cially in Colorado, where there is so much calcium carbonate pres¬ 
ent with which they can combine. Furthermore, it has been shown 
that bacteria and molds can utilize the salts of certain organic acids 
such as acetates, propionates, butyrates, citrates, malates, succi¬ 
nates, tartrates, valerates and formates as a source of energy, and 
ultimately reduce them to carbonates, carbon dioxide and water. 
It is indeed a rare occurrence to find arable land in this state which 
is acid, although a few such have been noted by Dr. Headden. 
When this does happen, it is due largely to the presence of the so- 
called “humic acids” and acid humates, complex organic com¬ 
pounds about which we have but little definite knowledge. A lib¬ 
eral application of lime or ground limestone to soils in this condi¬ 
tion usually alleviates the trouble in time. Blair states that the 
average acid soil of Florida requires 1,500 pounds of lime per acre 
to neutralize the acid to a depth of nine inches, yet it is not un¬ 
common to find peat and muck lands where the acidity is many 
times this amount. 
The alcohols produced are of considerable commercial im¬ 
portance as well as of scientific interest. They include ethyl or 
grain, propyl, butyl and iso-butyl alcohol. 
The changes produced in starches are very similar to those 
met with in the sugars. However, before any carbon dioxide, al¬ 
cohol, etc., can be set free, it is necessary to convert the starch into 
sugar. This is accomplished by a secretion from the microbial cells, 
called an enzyme, and the specific enzyme or ferment in this case 
is diastase. After this change is brought about, the fermentation 
and the products found are in all respects identical with those 
formed during the breaking down of sugars. 
Cellulose, which constitutes a large per cent of the weight of 
woody tissue, and of which the cell walls of young plants are com¬ 
posed almost entirely, is very useful in maintaining the proper phy¬ 
sical condition of a soil. Straw, cotton fiber and flax fiber are 
