1932] Poliak: Afferent Fiber Systems, Primate Cerehral Cortex 225 



Since the stimuli emanating^ from external objects are for the most 

 part of a complex nature, the ability of an afferent system to create 

 an "objective" impression and to transmit it in such a form to the 

 central or^an, to the cerebral cortex for example, will depend first on 

 the ability to ' ' decompose ' ' these complex stimuli into their elementary 

 constituents. That tendency to decompose or to analyze complex 

 external stimuli seems to be the meaning of the perfection of all the 

 higher aiferent systems concerned with radiant forms of energy 

 (stimuli). It is the elementary stimuli which when separately received 

 permit the finest and, accordingly, the most adequate judgment of the 

 nature of a certain composite stimulus. The task of the highly per- 

 fected sense organs and of their corresponding' nervous apparatus 

 seems, in general, to be to bring down the complex external stimuli to 

 their elementary components or to primitive stimuli and to transmit 

 these latter with as little change as possible to the central organ, 

 especially to the cerebral cortex. It is this latter place where the 

 arriving primitive stimuli or at most some simple combinations of 

 these are once more welded together to produce higher composite 

 forms of nervous activity of a very different character. The analytic 

 peripheral nervous process wdth subsequent central synthesis can be 

 compared with similar processes in digestion. Since the cells of various 

 organs are unable to utilize the nutritive material represented by 

 highly complex molecules, the latter must first be split into simpler 

 chemical units. In such simple form the nutritive material is made 

 suitable for resorption in the alimentary tract, for transport to the 

 places of its utilization and consumption by the cells of the organism. 

 In these latter the process of decomposition can take its further course, 

 or new more complex chemical units are made by a synthetic process. 



As to the concrete problem as to how far the organs of the senses, 

 their afferent paths, and perhaps also other parts of the central nervons 

 system exhibit in their architecture a reflection of the physical prop- 

 erties of various external stimuli has only occasionally been men- 

 tioned, in the preceding chapters. Further statement is likely beyond 

 surmise in the present state of our knowledge. 



In the light of the above explanation the various modes and degrees 

 of perfection of the afferent paths (including all finer changes in 

 internal structure and chemism) appear as being due primarily to 

 properties of the external stimuli to which they react. Where the 

 stimuli possess a "spatial" character (light, thermic, and sound 

 waves, gravitation, and similar forms of energy like inertia, and touch) 



