viii PREFACE TO THE SECOND EDITION 



out the wise counsel of one of its authors. Since the first edition of this 

 book was published Prof. Philip Hanson Hiss, Jr., has died. By his 

 death we have lost a dear friend and a valued teacher, and American 

 bacteriology has been deprived of a worker who was entering into the 

 most brilliant period of his scientific maturity. 



H. Z. 

 NEW YORK, 1914 



