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accommodation, a discovery previously made by Cramer, a pupil 

 of Donders. He also was busy with his researches on colour and 

 colour sensation. Thomas Young had previously asserted that red, 

 green, and violet, are the three primary colour sensations. Helmholtz's 

 attention was directed to the subject by Midler's doctrine of the 

 specific energy of nerves. His Handbuch d. physiologischen Optik 

 was published from 1856 to 1867 (2nd ed. 1885-1894). 



At Bonn (1856) and Heidelberg (1871) he devoted himself 

 largely to the study of the sense of hearing, and his great work, 

 Sensationsof Tone as a Physiological Basis of Music, appeared in 1863, 

 and his monograph (New. Syd. Soc.) on the Ossicles of the Ear in 

 1869. In 1871 he returned to Berlin to succeed Magnus in the Chair 

 of Physics. Here we need only remark that he was one of the 

 greatest men of the last century, and any one caring to read a full 

 account in English will find an excellent description of his work by 

 Professor J. G. McKendrick in the Masters of Medicine series (1899). 



CARL LUDWIG. 



1816-1895. 



BOEN in Witzenhausen, his studies were carried on in Marburg, 

 where he graduated and became Professor of Comparative 

 Anatomy in 1846. Zurich (1849), Vienna (1855), and Leipzig 

 (1865), were the other spheres of his activity. Prom each and all 

 of these centres his numerous pupils published under his direction and 

 guidance an amount of work the extent and originality of which is 

 probably unsurpassed. His own papers are epoch-making, and he 

 founded the largest school of physiologists of modern times. The 

 strongly physical trend of all his work helped to lay the foundation of 

 the modern school of physiological thought — the school of Du Bois- 

 Keymond, Helmholtz, and E. Briicke — a school opposed to the 

 " Vitalismus " of Johannes Muller. 



As I have written fully of the life-work of my master elsewhere — 

 Medical Chronicle, June, 1895, I will content myself with a reference 

 to some of his famous papers — e.g., that on the kidney and the 

 secretion of urine in 1845, his epoch-making conversion of the 

 hsemodynamometer of POISEUILLE into his kymographion in 

 1847, the instrument which first recorded the beating of the heart. 

 By adopting a principle which was first employed by the celebrated 

 James Watt, he applied the graphic method to the study of physio- 

 logical problems. Blood gases and a gas pump, the depressor, nerve 

 the chorda tympani and its action, the secretion of glands, lymph 



