PREFACE. 



THE work of Dr. Magnin, which was published in 

 Paris in 1878 and translated by the writer in 1880, 

 gave an admirable resume of our knowledge of the Bac- 

 teria at the date of its publication. But very consid- 

 erable progress has been made since, especially as 

 regards methods of manipulation, the comparative value 

 of various chemical reagents as "germicides" and anti- 

 septics, and the role of the Bacteria^ in infectious.,. dis- 

 eases. With a view to keeping the work fully up to 

 the progress of science in this direction, the writer 

 has added a chapter upon each of these subjects, 

 and one upon " Bacteria in Surgical Lesions " (Parts 

 Third, Fourth, Fifth, and Sixth). His name, therefore, 

 appears upon the titlepage as one of the authors of the 

 present volume. It has not been considered necessary, 

 however, to rewrite the chapters on Morphology and 

 Physiology (Parts First and Second). It is true that 

 the classification of Cohn, which was very properly 

 adopted by Professor Magnin, is only provisional, and 

 that certain recently discovered pathogenic species are 

 not included. But these will receive attention in Part 

 Fifth of the present volume ; and it would be pre- 

 mature to attempt a natural and permanent classifica- 

 tion of these minute plants, which are now engaging 

 the attention of numerous investigators in all parts of 



