8 Preface 



the systematic classification and identification of bacteria; 

 to the laboratory methods used in studying them; to the 

 chemistry and toxicology of their metabolic products ; to the 

 problems of infection and immunity; to the individual the- 

 ories of immunity; to the blood-serum therapy; to bacterio- 

 vaccination and the opsonic index; to complement-fixation; 

 to the bacteriology of water; to the bacteriology of foods; 

 to the bacteriology of the dairy ; to the bacteriology of sew- 

 age and the methods of its disposal ; to the relation of bacte- 

 riology to agriculture ; to the relation of bacteriology to the 

 public health; to veterinary bacteriology, and so on and on, 

 almost without limit. A dozen great international journals 

 in English, German, and French are devoted to the subject, 

 and weigh down our shelves with hundreds of ponderous 

 volumes of innumerable monographs and experimental re- 

 searches, and one becomes bewildered in his efforts to 

 "keep up" with the ever-expanding information. 



In the meantime the "Pathogenic Bacteria," diverted 

 from one after another of the fields it had pre-empted, but 

 for which it was not definitely intended, found and held its 

 own place as a medical book. 



As it became more and more clear that the original inten- 

 tion of the author was to be realized and the destiny of his 

 book was to be purely medical, it became equally clear that 

 the present revision must meet the requirements of that field 

 as completely and as perfectly as possible. 



In the past the "Pathogenic Bacteria" has been devoted 

 to the consideration of bacteria only When the author was 

 criticized because it had nothing to say about the higher 

 fungi and the Protozoa, he pointed out that the title de- 

 clared the contents of the work, and a change would be 

 inconsistent with the original purpose. 



There was always the feeling that the development of 

 Protozoology would soon make it necessary for the student 

 to have a text-book upon the Pathogenic Protozoa, and that 

 it would then become necessary to divorce the two subjects 

 again. As, however, knowledge of the protozoa engaged in 

 human pathology has not so expanded as to make this either 

 necessary or desirable, and as the future purpose of the 

 "Pathogenic Bacteria" is to meet the needs of students of 

 human medicine and pathology, it has become both desir- 

 able and practicable to change the original plan, depart from 

 the unwholesome consistency, and, without any important 



