FOREWORD 



THE art of agriculture has long been practised, but the 

 science of agriculture is of comparatively recent origin. 

 This science rests upon the fundamental sciences chem- 

 istry, physics, and biology. One phase of biology, bac- 

 teriology, has within the last three decades assumed a most 

 important relationship. The early researches of Pasteur, 

 Koch, and their successors opened the field of inquiry as 

 to the causation of animal disease. More recently, exact 

 knowledge of the influence of microorganisms on soil pro- 

 cesses, on dairying, and on foods in general has been greatly 

 extended. It is of the utmost importance for the farmer 

 and the student of agriculture to have a proper conception 

 of these relations. 



The purpose of the text here presented is to give to the 

 reader and to the student the essential facts concerning the 

 relation of microorganisms to daily life, and especially to 

 that of the farm, without a confusing mass of detail, both 

 chemical and biological, the presentation of which often 

 hides the essential information the student should gain. 

 The terminology is simple. Descriptions of specific or- 

 ganisms have been avoided; and, in general, the various 

 phases of the subject are presented in their broad outlines 

 in order to acquaint the student with the fundamental prin- 

 ciples, which can be applied to subjects not considered. 



A full conception of the relation of microorganisms to 

 agriculture can not be gained without working with them in 

 the laboratory. Without such experience the organisms 

 remain intangible to the student. Much can also be done 



