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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