PHENOMENA OF NEUROBIOTAXIS 

 I N THE O P T I C S Y S T E :M 



B T 



C. U. ARIÉNS KAPPERS 



AMSTERDAM 



DEDICATED TO THE GREAT SPANISH NEURÜLOGIST 

 S. RAMÓN Y CAJAL, ON HIS JO^" ANNI\ERSARY 



Nemo Deo, carisque parentibus 



atfjue magistris 



Gratias pro meritis dignas referre potest. 



Since the discovery of processes of taxis and tropism, these never 

 failed to attract the interest of investigators. After some general state- 

 ments concerning the significance ofphysical and chemical influences for 

 engendering and directing forms and motions in plants and animáis it was 

 especially the eighties of the preceding century that gave us a series of 

 precise observations concerning this matter. 



About that time Engelmann published his investigations on the tropism o 

 lower organisms. Angelucci and Kühne discovered the phototropic character of the 

 eyepigment and Van Genderen Stort shortly afterwards discovered the changes 

 in the rods and cones, when exposed to light. Pfeffer made observations on 

 chemotactic motions of seeds, bacteria and protozoa. MüHer-Hettlingen for the 

 first time acquainted us with the phenomena of galvanotropy in roots and Ver- 

 worn discovered similar phenomena in protists, whilst Loeb investigated light 

 tropisms, geotropism and the influcnce of gravitation on growth. 



Soon these tropisms were al so applied to the arrangement of the cells 

 in the living organism and when — now thirty years ago — S. Ramón y Ca- 

 /al's brilliant researches on the retina were published (La Cellide, tomeIX> 

 1892), the great Spanish histologist did not only give us a complete and 

 comparative survey of the minute structure of this senseorgan in Teleosts, 

 Amphibia, Reptiles, Birds and Alammals, but also in this respect Ramón 

 y Gzya/ought to be remembered with great veneration that he in this pa- 



