LETTER FROM HUMBOLDT. 229 



but that special action which we call organic, 

 in which every part becomes cause or effect, 

 seems to me distinct from the changes which 

 our planet has undergone. I pause here, for 

 I feel that I must annoy you, and I care for 

 you too much to run that risk. Moreover, a 

 superior man like yourself, my dear friend, 

 floats above material things and leaves a mar- 

 gin for philosophic doubt. 



Farewell ; count on the little of life that 

 remains to me, and on my affectionate devo- 

 tion. At twenty-six years of age, and pos- 

 sessed of so much knowledge, you are only 

 entering upon life, while I am preparing to 

 depart ; leaving this world far different from 

 what I hoped it would be in my youth. I 

 will not forget the Bichir and the Lepidosteus. 

 Remember always that your letters give me 

 the greatest pleasure. . . . 



[P. S.] Look carefully at the new number 

 of Poggendorf, in which you will find beauti- 

 ful discoveries of Ehrenberg (microscopical) 

 on the difference of structure between the 

 brain and the nerves of motion, also upon the 

 crystals forming the silvered portion of the 

 peritoneum of Esox lucius. 



