PREFACE. 



" IN the study of the microscopic forms known as bacteria we have 

 what might be fitly called the focal points of the various branches of 

 biological science. Though their investigation may require careful 

 morphological researches, yet the unmistakable monotony of form 

 combined with a considerable variation of physiological activity has 

 compelled the bacteriologist to pay much attention to means by which 

 such physiological variations may be more or less accurately registered 

 in order that they may serve as a supplementary basis for classification. 

 Again, with unicellular organisms the manifestations of cell activity 

 become the most important phenomena for study. These manifesta- 

 tions bring together the fields of physiology and chemistry and make 

 bacteriology in one sense a branch of physiological chemistry." 1 



" There is no ulterior interest in the study of bacteria as such, which 

 is a strong impulse in many other departments of biological science. It 

 is what bacteria do, rather than what they are, that commands atten- 

 tion, since our interest centers in the host rather than the parasite." 2 



The development of bacteriology has followed very closely the 

 gradual improvement of the optical parts of the compound microscope, 

 and to a lesser degree, the perfection of other instruments of precision 

 on the one hand, and the production of anilin dyes and a great expan- 

 sion of the fields of organic and physical chemistry on the other hand. 

 Naturally the greatest advances in bacteriology have been made along 

 the lines of morphology, staining and diagnosis, because the application 

 of the microscope, anilin dyes, and the preparation and use of cultural 

 media to bacterial problems is relatively simple and direct. The final 

 chapters of bacteriology, in which the problems of immunology are 

 of paramount interest, will be intimately associated with an unfolding 

 of the chemistry of cellular activity, as Theobald Smith has so clearly 

 pointed out in the opening paragraphs of this discussion. 



1 Theobald Smith. The Fermentation Tube, Wilder Quarter Century Book, 1893, 

 p. 187. 



2 Theobald Smith. Some Problems in the Life History of Pathogenic Microorgan- 

 isms, Amer. Med., 19Q4, viii, 711. 



