INTRODUCTION 



Bacteriology and Microbiology.— The science of Bacteriology 

 occupies a somewhat peculiar position among the natural sciences, 

 partly because of its recent development and partly because of the 

 overshadowing importance of its practical applications. As, 

 bacteria are microscopic plants, some have considered bacteriology 

 as a minor division of botany; but the methods of work and the 

 practical applications of bacteriology have little in common with 

 those of the more ancient science. Indeed were it not for the 

 importance of these little organisms to the chemist, the pathol- 

 ogist, the physician and the agriculturist, we should hear little 

 about them. 



The foundations of the science were laid by Pasteur (1858) 

 by the introduction of media and methods for artificial culture 

 of bacteria and the separation of mixtures into pure culture by 

 the laborious and uncertain but nevertheless successful method 

 of dilution in fluid media, thus making possible the accurate 

 experimental study of microbes. Robert Koch (1872-1882) con- 

 tributed much to the establishment of the new science by intro- 

 ducing the use of solid media and the method of plating for the 

 isolation of pure cultures and especially by his wonderful achieve- 

 ments in investigation of the pathogenic bacteria by his new 

 methods. Koch used potatoes, and aqueous humor and blood 

 serum rendered solid by the addition of gelatin. He first em- 

 ployed the aniHn dyes in staining bacteria (1877), microphotog- 

 raphy of bacteria (1877), homogeneous immersion objectives 

 and the Abbe illuminating apparatus (1878). Much of our 

 modern technic has been devised by his pupils and colleagues. 

 The commonly used meat-water-pepton-gelatin was introduced 

 by Loffler; agar by Frau Hesse. 



