PREFACE TO FOURTH EDITION 



In preparing this book I had in my mind the requirements of the 

 practitioner who has had but little or no training in bacteriology 

 and haematology, and who wishes to know what help may be 

 afforded him by these two sciences in his everyday practice. I 

 have tried to give clear and succinct information of the conditions 

 in which these new branches of pathological work may help him, 

 exact information how to proceed, and advice as to the circum- 

 stances in which it is necessary to have recourse to expert 

 assistance. The facts that three editions of this book have been 

 exhausted since its appearance in igo2, and that I have received 

 numerous and kind letters concerning it from practitioners in all 

 parts of the world, lead me to think that it has proved useful to 

 the class of readers to whom it was addressed. I have therefore 

 made comparatively slight alterations in this edition. It seemed 

 advisable to add an account of a simplified method for the 

 Wassermann reaction, which in my hands has yielded very good 

 results ; not so much because I think it should be carried out by 

 anyone who is not an expert, but because it serves as an intro- 

 duction to a matter of profound importance to every medical man 

 — the interpretation of the results of the test. This I have dealt 

 with at some length. Apart from this, the alterations in this 

 edition are mainly in matters of detail. 



I have, as before, to express my thanks to Professor Leith of 

 Birmingham and to Dr. Whitfield for many kind suggestions ; to 

 the latter for his photographs reproduced on Plates IV. and VI., 

 to Dr. Gompertz for Figs. 28, 31 and 42, and to Dr. H. B. Day 

 for Figs. 16, 17 and 18 ; and to Messrs. Baird and Tatlock, Swift 

 and Sons, Leitz, Zeiss, Hawksley, Down and Hearson for the 

 loan of blocks of apparatus. 



July, 1912. 



