ADDENDUM 



The first edition was only issued some two years ago, and 

 no material advances have been made since that date in the 

 branches of Public Health Bacteriology treated in this volume. 

 It is unnecessary therefore to completely revise the text, more 

 particularly as none of the recent work invalidates any of 

 the methods and conclusions given. 



A number of different investigations have been published 

 which extend and confirm the conclusions arrived at. In this 

 addendum only those advances and new methods which 

 facilitate the examination of the substances under considera- 

 tion have been selected and summarised. A number of other 

 procedures have been advocated, but they have not as yet been 

 sufficiently controlled to include them as methods of approved 

 value and utility. 



i. The Differentiation of the Streptococci. 



The organisms included under the term streptococci com- 

 prise such a large class, are responsible for so great an 

 amount of human disease, and are so widely diffused in nature 

 under saprophytic conditions that it is to be anticipated that 

 repeated attempts will be made to arrive at some trustworthy 

 methods for their differentiation. Such differentiation is as 

 essential from the Public Health standpoint as it is from the 

 more limited pathological aspect, since accurate means of 

 separating streptococci of human from those of animal origin, 

 and the saprophytic from the pathological types, would be of 

 the greatest service. 



