PREFACE TO THE FIFTH EDITION. 



DURING the three years which have elapsed since the publication 

 of the previous edition, important additions to knowledge have 

 been made in nearly every department of bacteriological research. 

 We have again endeavoured to incorporate these as fully as 

 possible, having in view our primary object, namely, to supply a 

 Manual for students and practitioners of medicine. 



It is impossible to refer in detail to the new matter introduced, 

 as this occurs in practically every chapter. It may, however, be 

 mentioned that in dealing with technique, we have introduced a 

 new chapter in which the more recent methods of investigating 

 the properties of serum and allied subjects are described. While 

 it is necessary for students of medicine to have a general know- 

 ledge of such subjects, those commencing independent bacterio- 

 logical research may benefit from the details given in this 

 department. 



\Vi- have also in the present edition grouped together in a 

 new chapter the pathological conditions with which spirochyetes 

 are associated, but as the biological relationships of these organ- 

 isms to kindred forms are still not completely determined, we 

 have retained this chapter in its former position. 



We have transferred the consideration of Yellow Fever to the 

 Appendices, which include diseases of protozoal origin and con- 

 lit ions in which the nature of the infective agent is still un- 

 known. In further following this principle, we have added 



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