vi PREFACE. 



observations of pure cultures obtained either from Krai's 

 laboratory or from the original discoverers of the bacteria. 



The subject of the bacterial flora of sewage is yet in its 

 infancy, but enough work has been done to enable certain 

 bacteria to be classed as the normal inhabitants of sewage, and 

 I hope this section will assist in the solution of the difficult 

 problems which are often placed before the water bacteriologist. 



Of the bacteria which give rise to specific disease in human 

 beings, only the B. typhosus and Sp. Cholene Asiaticae occur 

 sufficiently often in water to merit description in a small work. 

 The differential diagnosis of the B. typhosus by the serum test 

 has lately received much attention, and an attempt has been 

 made to summarise the most recent work on the subject. 



The plates have been drawn from my own sketches, and the 

 colonies depicted are believed to represent the forms most 

 commonly seen during routine examinations of " water-plates." I 

 have to thank Major Leishman, R. A.M.C., for kindly reading the 

 proofs, and for many valuable suggestions. I have further to 

 express my indebtedness to Dr. A. C. Houston, who has allowed 

 me to reproduce the descriptions of the sewage bacteria given in 

 his report to the London County Council ; and to Dr. Mervyn 

 Gordon for the use of his valuable paper on B. coli. 



W. H. 



SHOLING, SOUTHAMPTON. 



September 1901. 



