1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 219 



Chapter XIX 



AN ATTEMPT TO EXPLAIN STRUCTURAL FEATURES OF 



THE AFFERENT PATHS IN CONNECTION WITH 



THEIR FUNCTION AND THEIR BIOLOGICAL 



SIGNIFICANCE 



To understand the phylogenetic appearance of the afferent paths, 

 to explain their morpholog-ical peculiarities and their function, it is 

 indispensable to consider the general biological role such systems play 

 in the life of animals. Such a study will give clues as to why certain 

 neurons acquire the ability to receive and conduct special impulses 

 from without, and as to whether the internal organization of the 

 afferent paths stands in some causal relationship to the external 

 stimuli. In the present discussion of these problems our method will 

 be that of pure description and statement of facts with the realization 

 that the real inner causes — physical, chemical, neurodynamic, and so 

 forth, must of necessity, because of lack of data, remain unconsidered. 



Undoubtedly the appearance of afferent neuronic complexes with 

 specific functions must be caused by some special external causes, 

 which serve as the creative stimuli. (It must be granted that the 

 inherent properties of protoplasm enable such changes to occur.) It 

 could a priori be expected that the number of afferent paths will 

 approximatel}^ correspond to the kinds of the external stimuli. It can 

 also be expected that the nature or form of the physical and chemical 

 agents serving as stimuli will in some way or other be reflected in the 

 inner structures and, therefore, in a special mode of action of special 

 afferent systems. And lastly from the general biological view point, 

 there can be little doubt that each of the afferent paths together with 

 their special peripheral sense organs evolved in the course of phylo- 

 genesis will serve its own purpose in the life of the animal regardless 

 of whether a planful purpose was or was not originally intended. 



In some sense it can be assumed that every living being or indi- 

 vidual stands apart, in opposition to the entire surrounding world. 

 Yet being, nevertheless, a part of that surrounding as long as it exists 

 every individual stands in an incessant interrelationship to its environ- 

 ment, to which it must either adjust itself, or adapt that environment 

 to its own needs, or, most usually, act in both these directions. The 



