10 PREFACE TO THE SECOND EDITION. 



may and must leave much unsaid in order not to confuse; 

 but ever so short a text-book can only claim the designa- 

 tion of science if the student can follow the author's 

 thoughts. Besides, for the learner there is no greater 

 satisfaction, when he comes upon difficulties, than the 

 certain statement that, in a certain point, the imperfec- 

 tion of our knowledge, and not his inability, is the cause 

 of the difficulty. 



The fruitful labors of all investigators in the field of bac- 

 teriology made necessary a complete revision of the text in 

 both the general and special parts. In the general part the 

 discussion upon the causes of disease, disposition, and im- 

 munity is substantially extended. Beginning with page 

 119 is an exposition of the most important botanical points 

 of view which are important in classifying and properly 

 naming fission-fungi. In the special part, in fifty varieties 

 dependent upon autopsies, we have made additions and 

 improvements; about eighty varieties are newly intro- 

 duced. We have especially undertaken fundamentally 

 new work upon the causes of diphtheria and tuberculosis, 

 together with the related varieties. It is hoped that the 

 value of the atlas is essentially increased by the introduc- 

 tion of nine new plates, which replace three old ones 

 (diphtheria and the allied bacteria, varieties related to 

 the tubercle bacillus, gonorrhea, and pest). 



The literature of the past three years has been conscien- 

 tiously studied; many statements are substantiated, and 

 everything which seemed of importance in the publications 

 up to about June, 1899, is taken up. We hope that we 

 have made a proper selection from the almost immeasur- 

 able material, which increases daily. Perfection, naturally, 

 we cannot expect: some small mistakes and oversights 

 could not be avoided. The division of the work was the 

 same as in the first edition. 



K. B. Lehmann, 

 R. 0. Neumann. 



