Hermann Ludwig 

 Ferdinand von Helmholtz 



JOHN GRAY M'KENDRICK 

 \\\ 



M.D., LL.D., F.R.SS.L. AND E. 



PROFESSOR OF PHYSIOLOGY IN THE UNIVERSITY OF GLASGOW 



AND FELLOW OF THE ROYAL COLLEGE OF PHYSICIANS 



OF EDINBURGH 



L O ND O N 

 T. FISHER UNWIN 



PATERNOSTER SQUARE 



MDCCCXCIX 



