ORGANIC MOVEMENTS 27 



states or conditions have been inferred from this study, and, 

 so to say, have been projected upon the nervous system. 

 It was seen that simple nervous conduction would not 

 suffice to explain what happens here, and the word " centre " 

 therefore played a great though rather mysterious role. 

 " Centres " were identified with the anatomical ganglia until 

 Bethe showed that in crabs some typical reflexes may go 

 on even after the ganglia have been extirpated. A 

 certain school of modern physiologists then thought they 

 might drop the concept of a " centre ' : altogether, but more 

 recently a sort of compromise between the old and the new 

 theory has been come to. The concepts of " inhibition >: 

 and " path-making " (" Hemmung," " Bahnung," in German), 

 and the like have been employed to designate elemental 

 conditions of the nervous system, apart from conduction, 

 that are concerned in combined motions. 



The Concepts of von Uexkuell 



It seems to me that the system of elemental nervous 

 qualities which von Uexkuell 1 has lately created may 

 claim to be the most complete and the most original 

 conception in this field. To state in a few words the 

 logical value of von Uexkuell's concepts as relating to the 

 general theory of movement, it seems to me that he has 

 formulated what might be called the elemental " means " 

 in the mutual relation of the motor parts used and con- 



1 See especially Leitfaden in das Studium dcr experimented en Biologie der 

 Wassertierc, Wiesbaden, 1905. Von Uexkuell's work is composed of an 

 analytical and of an hypothetical or fictive part ; we only deal here with the 

 former, which is very valuable. This part will retain its value, it seems to 

 me, even if the hydrodynamic and electric hypothesis of " tonus " has to be 

 given up. 



