PREFACE TO THE SECOND EDITION. 



IN preparing the second edition of this book the 

 same principles have been followed as directed its 

 previous form. It has been found advisable to add 

 some more details concerning general disinfection, 

 the transmission of infection, especially in regard 

 to those diseases spread by insects, and the peculiar 

 phenomena of hypersusceptibility, a subject which 

 becomes wider in its significance as we learn more 

 about it. In regard to the special bacteria and diseases, 

 only such material has been added as was needed to 

 bring the book up to our present information. 



H. F. 



PHILADELPHIA, 1916. 



