102 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



abnormal central parts also, in the service of certain 

 " individualised * reactions that were needed. One could 

 hardly imagine a better illustration of the role of the 

 nervous system as a mere instrument for acting ; of course, 

 in the light of this discovery the so-called " motor spheres ' 

 also appear as anything but absolutely fixed ; l in any 

 case the organism may learn to use abnormal centripetal 

 nerves for its normal performances. 



I. THE LOWER BRAIN CENTRES IN VERTEBRATES 



To the whole of our discussion about the role of the brain 

 in acting in general a few remarks must be added concerning 



1 Flourens knew as early as 1842 that fowls use their wings in the right 

 way, if the two main nerves of the plexus brachialis are crossed by a 

 complicated operation. See also Spitzy, Zeitschr f. orthopdd. Chir., 1904, 

 vol. xiii. ; and Bethe, Munchner med. Wochenschrift, 1905, No. 25. Most 

 physiologists at present are strongly under the influence of materialistic 

 doctrines, and therefore try to conceive all complicated animal movement 

 as a mere sum of reflexes as far as possible. To such authors the formula 

 which von Uexkuell has given for certain very primitive motions (page 30) 

 was very welcome, and they sometimes have tried to found a general theory 

 on it. According to von Uexkuell's formula, in animals with "simple nerve- 

 nets " the state of the terminal (motor) organ determines the path of motor 

 stimulation, the "centres" work almost passively here as mere "reservoirs" 

 of "tonus." How absolutely impossible it is thus to understand Vulpius's 

 case, or the case of the dog walking on three legs, cannot be better shown, 

 it seems to me, than by simply alluding to the fact that all the movements 

 in question are notoriously under the influence of so-called "will," and 

 certainly do not take their origin from the periphery. (See also Giardina's 

 discovery, page 105, note 2.) Von Uexkuell's formula only holds good, 

 as he concedes himself, for rhythmical movements once set going, but never 

 for the origin or stopping or alteration of such movements. I can walk 

 almost mechanically and unconsciously, but I can also "will" to walk or 

 not ! In other words : Uexkuell's formula may explain a good deal of the 

 movements of an animal as far as these movements depend on the spinal 

 cord exclusively (see pages 30 and 103). But it never explains how abnormal 

 regulatory movements tending to a normal end are first established. When 

 once established, of course, these movements may again obey Uexkuell's law, 

 as far as their mere going on not their origin or stopping is concerned. 



