PREFACE. 



THE following book, with few additions, is a reprint of 

 a series of articles that have appeared in the Practitioner 

 (1884). Not pretending to be in any sense an exhaustive 

 treatise it will, I hope, nevertheless serve to illustrate most 

 of the important points bearing on investigations into the 

 life history of micro-organisms connected with infectious 

 diseases. 



I must not omit to mention that most of the investi- 

 gations recorded here were carried out for the Medical 

 Department of the Local Government Board during the 

 past ten years. 



E. KLEIN. 



