6 FROM THE PREFACE TO THE FIRST EDITION. 



look with suspicion upon a painted bacteriologic atlas. We 

 hope, however, that the unprejudiced critic will concede 

 that for certain objects (stab, streak, and potato cultures) 

 a well-colored representation surpasses the best photo- 

 graph, and that for a second group of pictures (plate- 

 colonies slightly magnified) a drawing, which can alone do 

 justice to the depth of the object, is at least equal to a pho- 

 tograph. We gladly acknowledge that for the representa- 

 tion of individuals magnified 1000 times photography is 

 the best method ; but there is now scarcely any doubt that 

 for the practical differential diagnosis of bacteria, only in 

 somewhat rare cases is the picture of the individual of 

 primary importance. We have, moreover, sought to take 

 advantage of the photographic method when the individ- 

 uals were to be represented, by comparing the splendid 

 photographs in the atlas of C. Frankel and R. Pfeiffer, and 

 also those in the literature (by Loffler, Heim, Roux, etc.), 

 with our own preparations. 



The choice of varieties for illustration was often very 

 difficult. To our great pleasure, we were able to present, 

 with the exception of about 4 per cent. , only originals in 

 the atlas ; while, naturally, those required as supplements 

 to the text are more often copies. In the latter case the 

 original source is always given. Varieties important from 

 a medical standpoint, especially when they present any 

 visible characteristics, could scarcely be omitted; also, 

 almost all varieties pathogenic for animals are introduced. 

 Chromogenic, zymogenic, and saprogenic bacteria were 

 never, to our knowledge, so extensively represented be- 

 fore; nevertheless, in this portion a careful choice was 

 required. We acknowledge that some among those selected 

 might have been omitted, and others chosen. 



The text is divided into a general part, which I have 

 prepared alone, and a special part, in which I have re- 

 ceived the constant cooperation of Dr. Neumann. 



The general part furnishes a condensed survey of the 

 principal properties of bacteria so far as they are of prac- 

 tical value, especially so far as they are of diagnostic aid. 

 It is assumed that the reader has mastered the ordinary 

 elements of bacteriologic technic, but at the request of the 

 publisher we have appended a short list of media rules for 



