Mental Processes in Man. 303 



co-ordination of muscular activities. And anatomical 

 investigation shows us that in such creatures there is 

 always, in the course of the channel of communication or 

 transmission, a group of closely connected cells, which 

 play the part of co-ordinants. In the vertebrate animals 

 these co-ordinants are collected in the brain and spinal 

 cord. In the insects, crustaceans, and worms they are 

 arranged in a knotted chain running close to the under 

 surface of the body. To this central nervous system, as it 

 is called, nerves (afferent nerves) run inwards from the 

 recipient organs. From it nerves (efferent nerves) run 

 outwards to the organs of response. And in it the trans- 

 mitted stimuli, brought in by the afferent nerves, are 

 modified, through intervention of the co-ordinants, into 

 stimuli carried out by the efferent nerves. A simple 

 stimulus may create a great commotion among the co- 

 ordinants of the central nervous system, and give rise to 

 many and complex stimuli going out to the muscles and 

 other organs of response. How this is effected is one of 

 the many wonders of the animal mechanism. We believe 

 that the connection and co-ordinations have gradually been 

 established during a long process of development and evo- 

 lution, reaching back far into the past. How, we can at 

 present scarcely guess. 



We must picture to ourselves, then, in the animal 

 organism, a multitude of nerve-fibres running inwards 

 from all the end-organs of the special senses, from the 

 muscles, and from the internal organs, and all converging 

 on the central nervous system. And we must picture to 

 ourselves a multitude of nerve-fibres passing outwards from 

 the central system, and diverging to supply the muscles, 

 glands, and other organs which are to respond to the 

 stimulation from without. We must picture the fibres 

 coming from or going to related parts or organs collecting 

 together to form nerves and nerve-trunks, which are, 

 however, only bundles of isolated nerve-fibres. And, 

 lastly, we must picture the central nerve-system itself 

 co-ordinating and organizing the stimuli brought into it 



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