24 HERMANN VON HELMHOLTZ 



' I am working hard at my thesis. Once I thought I had 

 arrived at a conclusion of the utmost importance ; on closer 

 observation the day before yesterday I found the contrary, 

 and then on looking into it again more carefully yesterday 

 discovered that the first idea was right with certain limita- 

 tions. To-day I am going for the point more carefully/ His 

 only recreation from this labour was the Art Exhibition, and 

 he greatly admired Lessing's Huss, l a picture that is perhaps 

 worth more than all the earlier exhibitions put together; at 

 any rate here in Berlin we have no picture so profound, so 

 inspired, and so characteristic. Every one is charmed with 

 it, except the Berlin professors/ 



M tiller ultimately declared the thesis to be satisfactory, and 

 Helmholtz took his doctor's degree on November 2, 1842 ; his 

 Inaugural Dissertation, De Fabrica Systematic Nervosi Everte- 

 braforum, or 'The Structure of the Nervous System in 

 Invertebrates', being dedicated to Johannes Miiller. His 

 microscopical discovery, that the nerve-fibres originate in the 

 ganglion cells discovered by Von Ehrenberg in 1833, has been 

 recognized by all physiologists as the histological basis of 

 nervous physiology and pathology: the connexion till then 

 sought in vain between nerve-fibres and nerve-cells, and there- 

 with the proof of the central character of these cells, was 

 established by him for invertebrates in this first-rate contribution 

 to minute anatomy. 



As soon as Helmholtz had overcome the initial difficulties of 

 his post, he devoted himself gladly to his calling, but managed 

 to find time to pursue the many-sided studies of the previous 

 year, and develop them profitably. He became so absorbed 

 in his work that he could not tear himself away, and for the 

 first time failed to convey his birthday congratulations in person 

 to his father. In writing, he refers the older man (who cared 

 little for practical realities) to the ideals of a brighter future, 

 but his own scientific thoughts were turning more and more 

 away from the metaphysical, idealistic views by which science 

 was then held in bondage. He directed his hopes entirely 

 to the real world, the world of fact, thus laying the foundation 

 of the mighty structure which was to be erected in the second 

 half of the nineteenth century. 



The theoretical methods which obtained in that period of 



