PREFACE. 



THE organisms considered in agricultural bacteriology are 

 specifically the most numerous, chemically the most active, and 

 economically the most important known. This being true, why is 

 so much interest shown in the injurious and so little in the beneficial 

 bacteria? There are two chief reasons for this condition. When 

 an outlaw' commits some crime against human society it is heralded 

 far and near and the machinery of the law is set in operation to 

 apprehend the culprit and bring him to justice. So it is with these 

 outlaws in bacterial society. The typhoid, or perchance some other 

 disease-producing organism, attacks some individual, or it may be 

 an entire community. If it be typhoid, we hear of the long-drawn- 

 out fight between the human individual on the one hand and the 

 invisible enemy on the other. If disease be not checked it spreads 

 to other places, and, as in the Dark Ages, sweeps like a prairie-fire 

 over a whole continent or, as recently, over the entire world. The 

 second reason why we hear more of the disease-producing organisms 

 than we do of the beneficial bacteria is that man has learned that 

 it is a fight between him and these microbes to determine which 

 shall inherit the earth. He has learned that he must protect him- 

 1 self against these enemies. For these reasons man has studied the 

 bacterial outlaw, his place and condition of growth. 



On the other hand, though we admire the magnificent structures 

 and complex institutions which have been reared by the mind and 

 hand of men, we see and pass on. In many cases we do not stop to 

 contemplate the countless millions, living and dead, who have 

 contributed their mite that things might be as they are. Man does 

 not have to protect himself against these honest toilers ; hence, they 

 go unnoticed. The work of the benefactor lacks the sensationalism 

 which is attached to that of the destroyer. So it is with the count- 

 less billions of beneficial bacteria; they toil on day and night, 

 generation after generation, accomplishing good for the human race. 

 We do not miss them, for they have always helped us. They never 

 become discouraged, but work for our good until conditions become 

 intolerable, when they die to be in many cases replaced by the 

 bacterial outlaw. 



If the following pages help to systematize, to arouse interest, to 

 stimulate curiosity or inquiry in even a small degree in this intensely 



