PREFACE ix 



greatly encouraged us at an early stage of our work with his favorable 

 observations of living cancer cells by means of our initial phase micro- 

 scopic equipment. We wish to express our indebtedness to Mr. Bryant 

 Glenny, Jr., General Manager of the Instrument Division, American 

 Optical Company, Buffalo, New York, for his encouragement through- 

 out our investigations. This work would have been incomplete without 

 the cooperation of many of the world's outstanding makers of micro- 

 scopes and allied equipment. These manufacturers have kindly sup- 

 plied the illustrations of commercially available phase microscopes. 

 Accordingly, the authors wish to express their thanks and deep obliga- 

 tions to the American Optical Company, Bausch and Lomb Optical 

 Company, Cooke, Troughton and Simms, Ltd., Henry Wild Surveying 

 Instruments Supply Company, Ltd., Winkel-Zeiss, Officine Galileo, 

 Koristka, and C. Reichert Optical Works for their permission to use the 

 illustrations of the equipment. 



Alva H. Bennett 

 Director of Research 

 Research Laboratory 

 American Optical Company 

 Stamford, Connecticut 

 August, 1951 



