312 Journal of Comparative Neurology. 



an index of action, since it is seen in non -nervous tissues also 

 (the muscles). 



The physiologically simplest and best known neurones are 

 the segmental motor ones. On their integrity depends the ob- 

 jective demonstration of all disorders of other neurones. The 

 afferent neurones can be analyzed indirectly only, as far as their 

 individual function goes. It is not improbable that the specific 

 function of the afferent neurones depends on the segmental and 

 suprasegmental connections of the mechanisms. 



Considerations based on comparative neurology and on the 

 results of experimental anatomy recommend the adoption of a 

 plan of the nervous system which favors the study of functional 

 mechanisms. Instead of starting from the most differentiated, 

 most complex, and anatomically least known cerebral centers, 

 we take the segmental motor neurones as a basis, those neu- 

 rones which grow in the basal lamina af the neural tube (or 

 neural stem) on either side of the raphe, and connect through 

 their axone with definite muscle fibers, blending with them to a 

 functional and even trophic unit. We divide them into seg- 

 ments according to the * peripheral nerve-roots ' and their func- 

 tion. Afferent neurones from the spinal and cranial ganglia 

 combine with them to form segmental mechanisms with the 

 help of intermediate (association or rather dissociation) cells. 

 Differentiation of function is obtained by the growth of specially 

 connected mechanisms, probably working so, that the (first) 

 cells of the mechanism ' learn ' to react mostly to the stimuli 

 serviceable to the function of the whole organism. The simile 

 was used that the cell is 'attuned' to special stimuli only. Apart 

 from the segmental and intersegmental mechanisms, we have 

 found suprasegmental mechanisms, anatomically lifted out of 

 the neural stem as cerebellum, midbrain-ganglia and thalamo- 

 cerebrum. On ground of the experimental data we recognize 

 in them i. the body of the special organ, 2. the afferent neu- 

 rones (* intermediate neurones ' of the segments sending their 

 processes into the special organ) and 3. efferent neurones (cells 

 of the special organ sending their fibers into the segments or 

 into the other suprasegmental mechanisms). The advantage of 



