CHEMICAL CHANGES PRODUCED BY MICROORGANISMS 25 
these organisms are so closely associated with phenomena is be- 
cause they are capable of bringing about profound chemical 
changes. 
From facts already considered it will be evident that micro- 
Srganisms have properties that certainly fit them for this work. 
They feed, not upon minerals, as a rule, but upon the organic 
material in nature; and each kind of organic food, proteid, sugar, 
starch, wood, etc., is especially subject to the attack of one of the 
classes of fungi. We have seen also what inconceivable powers of 
multiplication are possessed by bacteria, and, while the other or- 
ganisms do not grow so fast, they are all rapid growers. While 
they are growing and multiplying with such vigor, they are produc- 
ing profound changes in the chemical nature of the food upon 
which they are feeding. 
CHEMICAL CHANGES PRODUCED BY MICRO- 
ORGANISMS 
The chemical changes thus brought about are very numerous. 
The chemist of to-day has hardly begun to study them, and his 
knowledge is, as yet, very fragmentary. Only a very few of them 
are understood, and in regard to the simplest of these our knowl- 
edge of the phenomena is yet lacking in many important respects. 
A few only, bearing directly upon the subject of agriculture, will 
be explained. They may be grouped under two quite distinct 
heads. 
Synthetic Processes. Anabolism.—These consist in the build- 
ing of complex bodies out of simpler ones. The fundamental 
importance of synthetical processes to the continuance of life is 
evident enough. ‘The animal kingdom, in general, demands com- 
plex compounds as foods, and cannot live upon the simple com- 
pounds found in the air and the soil, like carbonic dioxide, nitrogen, 
ammonia, etc. (COs, N, NH3). In order that animals may use 
the elements existing in nature, some process must build them into 
