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years. He was also enriching Physiology in other directions, even 

 though well-nigh exhausting his strength in doing so : for he had 

 been also serving the University as Rector, an office which he re- 

 linquished in 1853.* In conjunction with Dr. Bauduin he undertook 

 a Manual of Physiology, which, however, he could only carry as far 

 as the first volume, ' Special Physiology ' (1853) for its time a 

 work of authority, and still the best record of contemporary teaching. 

 In 1857, he discovered that in each vowel sound the mouth is tuned 

 to a definite pitch, alike in men, women, and children using a 

 common speech, and differing only with difference of dialect ; this was 

 confirmed by Helmholtz. Again, in 1865, Bonders took the first step 

 in a new field of research, by determining the rapidity of perceptions 

 of Thought and of the Will. Others had arrived at the physiological 

 time, or that required for reacting by a movement on a nervous irri- 

 tation. But in the next succeeding years he carried these exquisite 

 investigations much further, analysing the time taken in simple, and 

 also in many and various complex, psychical processes, by a most 

 ingenious and refined method, which he explained in 1876, at one of 

 the Conferences at South Kensington in connexion with the Loan 

 Collection of Scientific Apparatus. t Others of his physiological 

 papers deserving special mention, among a great number, were : " On 

 the timbre of the Vowels," "Muscular Work and Development of 

 Heat in relation to the necessary Elements of Food," " On the 

 Tongue-instruments in the Organs of the Voice and Speech," 

 " Influence of the Vagus Nerve on the Cardiac Movements," " On 

 Associations, congenital and acquired " (the latter are the result of 

 habit in the individual, the former represent habit in the species), 

 " The Chemical Phenomena of Respiration are a Process of Dissocia- 

 tion;" indeed, to the close of his life he remained indefatigable in 

 the domain of Physiology, almost continuously winning new laurels 

 in one or other of its departments. 



In 1862 an event had occurred having an important influence in 

 this direction. By the death of Schroeder van der Kolk the chair of 

 Physiology fell vacant, and it was immediately pressed upon his 

 acceptance, with the understanding that a new Physiological 

 Laboratory should be erected for his use. This was an appeal he 

 could not withstand, though aware that it would involve a partial, 

 and, gradually, an almost complete, relinquishment of his ophthalmic 

 practice. But Physiology in its widest range, with the ample field 

 it presented for Research, had been his first love, and to this his 

 inclination now gradually led him back. His esteemed pupil, Snellen, 

 became his colleague at the Hospital, and eventually succeeded him 

 there ; while Thomas W. Engelmann, who was to be in course of 



* Vide note *, ante, p. IT. 



t Vide ' Science Conferences,' 1876, Section Biology, pp. 224228. 



