88 HERMANN VON HELMHOLTZ 



After sending the account of his experiments on the graphic 

 record of the rate of nervous transmission in the frog to 

 Johannes Miiller for the Archiv, he employed the Christmas 

 holidays, and the first weeks of the New Year, in writing 

 a report (originally intended to be a popular lecture), at the 

 request of Karsten, upon ' Recent Developments in Animal 

 Electricity '. On February 2 he tells du Bois that in reading 

 his book with the aim of summarizing the work on animal 

 electricity, he has discovered a theorem which seems to him 

 completely to resolve the difficulties as to the co-ordination 

 of the different elements of a muscle; by a combination of 

 the laws of electric potential and of the superposition of 

 currents, he had succeeded in proving that when electromotive 

 forces are distributed in any way in any conductor, all external 

 action exerted by the conductor, i. e. all the derived currents 

 which it excites in any linear or non-linear circuit, may 

 be replaced by a distribution of electromotive forces upon 

 its surface, just as the external action of a magnet can be 

 stated in terms of the distribution of magnetic fluid upon its 

 surface. 



In the meantime the Prussian Ministry were not slow to 

 accept the recommendation of the Medical Faculty, and to 

 appoint Helmholtz, who was now recognized everywhere as 

 a physiologist and physicist of the first rank, to be Ordinary 

 Professor of Physiology, which he became by Royal Brevet 

 on December 17, 1851. 



While he was busying himself with the required Inaugural 

 Dissertation, for the subject of which he turned to the Physio- 

 logical Theory of Colour, Part II of his great work on the 

 physiology of nerve and muscle appeared in Muller's Archiv 

 under the title ' Measurements of the Rate at which Excitation 

 is transmitted in Nerve'. In Part I he had already proved, 

 by means of the electro-magnetic method of time-measurement, 

 that the mechanical response of a muscle made its appearance 

 later after excitation of the nerve, when the excitation had 

 to travel through a longer portion of nerve before reaching 

 the muscle, but the application of this method involved pro- 

 tracted experiments, and necessitated a favourable condition 

 of the frog's tissues, on account of the long duration of the 

 experiments. He now endeavoured, with a graphic method 



