CHEMICAL CHANGES PRODUCED BY MICROORGANISMS. 23 
From facts already considered it will be evident that micro- 
organisms 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 producing 
profound changes in the chemical nature o 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 knowledge 
of the phenomena is yet lacking in many important respects. A few 
only, bearing directly upon the subject of agriculture, will be ex- 
plained. They may be grouped under two quite distinct heads. 
Synthetic Processes. Anabolism. These consist in the 
building 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 complex 
compounds as foods, and cannot live upon the simple compounds 
found in the air and the soil, like carbonic dioxide, nitrogen, am- 
monia, etc. (CO 2 , N, NH 3 ). In order that animals may use the 
elements existing in nature, some process must build them into 
complex bodies. This is largely accomplished by the green plants 
that furnish animals with food. But even these plants demand 
some of their food in a complex form, not being able, for example, to 
use nature's free nitrogen store in the atmosphere until it has been 
built up into some compound like nitric acid. The constructive 
or synthetic processes are thus of fundamental importance to the life 
