PREFACE BY TRANSLATOR. 



edge of the bacteria, by Dr. Magnin, of great assistance 

 to me, in pursuing the investigations in which I have 

 been engaged during the past year under the auspices 

 of the National Board of Health, it has seemed to me 

 that a translation of the work into English and its publi- 

 cation in this country would be productive of good in 

 more ways than one, and of the advancement of science. 

 To the naturalist, it cannot fail to be of value, as the 

 most approved classification, that of Cohn, is given, 

 with a full description of species. To give additional 

 value to this portion of the work, figures of many of the 

 best-known forms, drawn from various foreign sources, 

 and reproductions of some of my own photo-mico- 

 graphs (by permission of the National Board of Health), 

 have been introduced. 



If we are to judge from the scanty literature of the 

 subject in this country, the amount of interest which 

 has been aroused by the revelation of a new world of 

 micro-organisms, and by the momentous questions which 

 have been raised in connection with them, is far below 

 that awakened in Germany, France, and England. This 

 is not, however, really the case ; for, while we have but 

 few active workers in the difficult fields of inquiry 



