WHAT ARE MICROORGANISMS? 5 
largely adopted all over the world; but they have generally been 
adopted by farmers in ignorance that they are benefiting from 
bacteriological research. That these practical applications of 
bacteriology to agricultural processes will increase with the next 
few years is certain. Successful agriculture of the future is in- 
dissolubly bound up in the problem of the proper handling of 
microorganisms. We have reached a point where every advanced 
farmer, who wishes to put himself into a proper condition to make 
the best use of the means at his disposal and to profit by discoveries 
as they are made, must at least have a general knowledge of the 
fundamental factors of bacteriology as they are related to agriculture. 
WHAT ARE MICROORGANISMS? 
In studying the relation of germ life to the farm we are concerned 
with a class of phenomena called fermentation, putrefaction, decay, 
decomposition, and the like (see Chapter II). These phenomena 
are all caused by living bodies that are frequently called microorgan- 
isms. This term strictly means animals or plants of microscopic 
size. But this conception of the term is at once too narrow and too 
broad to cover the organisms we are to study. Some microscopic 
organisms have no particular relation to the classes of phenomena 
which we are considering. A great host of microscopic, green 
water-plants and also many microscopic animals have nothing to do 
with our subject, though they might properly be called micro- 
organisms. On the other hand, some plants of large size, like molds 
and toadstools, have a part to play in producing the decomposition 
of organic structures very similar to that played by bacteria. These 
cannot properly be called microorganisms, but nevertheless they 
must be included with the study of bacteria and yeasts, since they 
perform similar or closely allied functions in nature. A better term 
to cover the organisms which we must study might be the rather 
broad term of Fungi, for all of the organisms with which we are 
concerned belong to this general class of plants. But this term is 
also unsatisfactory, since it fails to convey the idea that the organisms 
are largely microscopic. To most people the term fungus gives at 
