PREFACE. 



To set any exact limits to Agricultural Bacteriology is diffi- 

 cult Primarily the subject includes only phenomena pro- 

 duced by bacteria, and phenomena that especially affect agri- 

 culture. 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 dis- 

 cussion 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 pro- 

 duced 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 bacterio- 

 logical 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 it 

 will, therefore, be necessary to consider, to a certain extent, 



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