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 indus- 
trial phenomena that they cannot be separated. Agriculture 
grades by imperceptible degrees into numerous secondary indus- 
tries. 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 fol- 
lowing pages, therefore, it will be necessary to consider, to a cer- 
tain extent, both types of fermentation. While both must be 
described and discussed, the bacteriological fermentations will 
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