viii PREFACE 



underlying its production. Great advances have been 

 made since the first early guesses that the light was due 

 to phosphorus and was a kind of oxidation. Although the 

 problem cannot be considered as solved, it has been placed 

 on a sound physico-chemical basis. Some material is 

 oxidized. Exactly what this material is and why light 

 accompanies its oxidation are the two more fundamental 

 problems in the field of Bioluminescence. How far and 

 with what success we have progressed toward a solution 

 of these problems may be seen from a perusal of the 

 following pages. 



It gives me pleasure to acknowledge the kindness of 

 Dr. W. E. Forsythe of the Nela Institute, Cleveland, Ohio, 

 in reading and criticizing the manuscript of Chapter III, 

 and of Professor Lyman of Harvard University for a 

 similar review of Chapter II. I am also deeply indebted 

 to my wife for reading the proof and to Dr. Jacques Loeb 

 and Prof. W. J. V. Osterhout for many suggestions 

 throughout the book. My thanks are also due to Prof. 

 C. Ishikawa of the Agricultural College, Imperial 

 University of Tokio, Japan, for his generous assist- 

 ance in providing Cypridina material. Finally I wish to 

 acknowledge the support of the Carnegie Institution of 

 Washington, through its director of Marine Biology, Dr. 

 Alfred G. Mayor. Without this support much of the work 

 described in this book could not have been accomplished. 



E. N. H. 



Princeton, N. J., 

 October, 1919. 



