PREFACE TO FIRST EDITION. 
To set any exact limits to Agricultural Bacteriology is difficult. 
Primarily the subject includes only phenomena produced by 
bacteria, and phenomena that especially affect agriculture. But 
some agricultural processes are so closely bound with other industrial 
phenomena that they cannot be separated. Agriculture grades 
by imperceptible degrees into numerous secondary industries. 
Quite a number of the phenomena which will be considered in these 
pages have a closer relation to these secondary industries than 
they do to agriculture proper, but nevertheless they do have at 
least an incidental relation to the farm and must, therefore, be 
included in a discussion of Agricultural Bacteriology. 
It has, moreover, in recent years, been a growing conviction that 
a considerable number of phenomena, hitherto attributed to bacteria, 
are directly due to a class, of chemical ferments called enzymes. 
These enzymes are sometimes produced by bacteria, but in other 
cases by organisms totally unrelated to bacteria. When the latter 
is the case the fermentations produced by them have, of course, 
nothing to do with bacteriology proper. But we do not know 
as yet how commonly these enzymes, or chemical ferments, are 
concerned in agricultural processes, and even where they do occur 
it is found that, in some cases, they are intimately associated with 
true bacteriological action. It is impossible to separate chemical 
from biological fermentations by a hard and sharp line, nor can we 
tell to-day how far both of them may be concerned in any particular 
type of fermentations. In the following pages, therefore, it will 
be necessary to consider, to a certain extent, both types of fermenta- 
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