32 Foster, Physical Basis of Psychical Events. 



modified epithelial cell, receptive of the external influence, 

 the stimulus, and one kind of end, a muscular fibre, or a 

 gland cell, or some analogous structure, something 

 outside the nervous system itself, on which the terminals 

 of the final axon play. Every cell within the whole nervous 

 system, be it in the spinal cord or lower cerebral structures, 

 be it in the cerebral cortex is, I repeat, essentially one link 

 in the chain which begins in a sensory receptive cell, and 

 ends in a motor or analogous effective cell. The funda- 

 mental action of the nervous system, whether the links be 

 many or few, is government of the effective cell by the 

 receptive cell ; the most common mode of government is an 

 activity of the effective cell in response to changes in the 

 sensory cell. In the simplest form, where the chain consists 

 of one link only, of one nerve cell intercalated between the 

 receptive and the effective cells, where the activities of the 

 whole mechanism are limited to mere degrees of activity of 

 the nerve cell and to the specific activities of its two agents, 

 the response of the effective cell to changes in the receptive 

 cell is simple and direct. As link is added to link, each new 

 link, with its differential characters, enlarges the potenti- 

 alities of the whole mechanism, rendering the dependence 

 of the effective on the receptive cell more and more indirect. 

 In the simple mechanism, response of the effective cell to 

 events in the receptive cell is almost imperative, and is 

 largely shaped by those events. In the complex mechanism, 

 not only the character of the response, but also when it comes 

 or whether it comes at all, is determined mainly by what 

 takes place in the chain of links. In the one case, the event 

 is flashed straight across the one link ; in the other, it is 

 reflected and refracted among a multitude of links, until 

 often it seems to be lost in the nervous system itself 



To this, the visual nervous chain is no exception. The 

 primary fundamental use of the chain is to govern 

 effective units, which are, in the main, muscular units. 



