26 FERMENTATION, PUTREFACTION, AND DECAY 
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 nitricacid. The construct- 
ive or synthetic processes are thus of fundamental importance to 
the life processes of both animals and plants. Among the chemi- 
cal changes which are brought about by bacteria, some are of this 
synthetic character. 
Analytical Processes. Decomposition: Katabolism.—The 
most noticeable action of bacteria is that of decomposition. The 
great majority of them, just like animals, live upon complex chemi- 
cal foods, and these compounds are broken to pieces by their action 
and reduced to simpler molecules. Acting in this way, the fungi 
are the most important agents in nature for reducing to a simpler 
condition the great quantity of organic matter which would other- 
wise accumulate upon and within the soil, or in bodies of water. 
The chemistry of the decomposition of organic substances is still in 
its infancy, and as yet only the general nature of the changes is 
understood. ‘The decomposition of these compounds in general 
brings the elements back to simpler conditions and nearer to the 
form in which they can serve as food for ordinary plants. 
Both synthetical and analytical processes are carried on, to a 
certain extent, by all bacteria. If they grow and multiply they 
must be manufacturing proteid and protoplasm out of the food 
products, for each new bacterium is made of protoplasm. This 
building of protoplasm is a synthetic process, and is, of course, 
characteristic of all growing bacteria. On the other hand, all 
bacteria likewise produce a certain amount of decomposition of 
the materials which serve them as food, giving rise to simpler prod- 
ucts as excretions. But while all bacteria thus perform both 
types of chemical change, the decomposition activity is, in general, 
much greater than that of synthesis; they are destructive rather 
than constructive agents. 
