42 THE AMERICAN MONTHLY [Feb. 



members of the American Microscopical Society feel un- 

 der deep obligation to him for help and suggestion. He 

 has not only used this beautiful art for scientific purposes 

 but has made excellent use of it in demonstrating the 

 truth of his conclusions in courts of justice. 



After receiving the degree of M. D. from the Syracuse 

 University in 1878, he spent about two and one-half 

 years in St. Thomas Hospital and Medical vSchool in Lon- 

 don, England, where he was a pupil in pathology of Dr. 

 W. S, Greenfield, now professor of pathology in the 

 University of Edinburgh. After becoming assistant to 

 Dr. Greenfield in the Brown Institution, Dr. Mercer cut 

 and mounted the first sections of tuberculous joints 

 studied in England and furnished the material described 

 by Mr. John Croft in Vol. xxxii (1881) of the transac- 

 tions of the Pathological Society of London. 



While in London he became . acquainted with Dr. 

 Lionel S. Beale, and revised for liim "Part V., On 

 taking Photographs of Microscopic Objects" of his well 

 known book, "How to work with the Microscope." On 

 Dr. Beale's nomination he was made a fellow of the 

 Royal Microscopical Society. He found a warm personal 

 friend in the late Dr. John Matthews, editor of the second 

 edition of the "Preparation and Mounting of Microscopi- 

 cal Objects," by Thomas Davis, and always recalls with 

 gratitude the demonstration Mr. John E. Ingpen gave 

 him of the Abbe diffraction theory of microscopic vision. 

 This was before the theory had become generally known 

 to the microscopical world. 



During this period and a subsequent visit to London 

 for professional study. Dr. Mercer had the good fortune 

 to be brought in friendly relations Avith Dr. Pt. L. Maddox, 

 Mr. E. M. Nelson and Mr. Andrew Pringle, England's 

 most skillful photo-micrographers. With a mind pre- 

 pared and open as was Dr. Mercer's the association with 



