PREFACE 



IN writing this book I have attempted to give a connected and 

 symmetrical outline of the chief facts definitely known with regard 

 to the method in which the body protects itself against infections, 

 and of their applications in the diagnosis, prevention, and treat- 

 ment of disease. It is not written in support of the views of any 

 particular school of thought, and, when dealing with subjects still 

 under discussion, I have tried to give a fair and impartial, though 

 necessarily succinct, account of each of the rival theories. The 

 factors in many of the problems of immunity are so complex, 

 and our knowledge of the subject grows and alters so rapidly, 

 that it is quite impossible to deal with it dogmatically at the 

 present time. I have kept in view, as far as possible, the re- 

 quirements of the physician and surgeon who may require an 

 epitome of the theoretical basis of the modern methods of diagnosis 

 and treatment, now assuming so much importance, and of the 

 student who desires a general survey of the subject before com- 

 mencing more advanced studies. 



My best thanks are due to Mr. H. K. Lewis for the ready and 

 courteous way in which he has acceded to all my suggestions and 

 requirements ; to Drs. Whitfield and Briscoe, from whom I have 

 received some valuable suggestions; and to Professor Herbert 

 Jackson, of King's College, for kindly reading the sections dealing 

 with the more purely chemical and physical questions and for 

 much useful information connected therewith. I have also to 

 thank Sir Almroth Wright and Drs. R. W. Allen, Eyre, and 

 Bolduan; Messrs. Macmillan and Co., Kegan Paul and Co., and 

 the proprietors of the Lavcet, British Medical Journal, and the St. 

 Bartholomew's Hospital Journal for permission to use illustrations 

 from their publications. 



