Neural Integration 173 



external world, but because of their situation subject onlv 

 to stimuli "given by the orrranisni itself." Spcciticallv the 

 sources of the stimuli are the muscles, joints, blood vessels 

 and so on, which by the regular activities are always in 

 more or less movable contact with one another and with 

 other parts and organs. Stimuli from the environment 

 acting upon the skin receptors give rise to reflexes which 

 put muscles into activity, and these activities serve in turn 

 as stimuli to receptors in the deep parts; and the impulses 

 arising from these deep receptors may pass to still other 

 muscles over the same effector neurons used bv im})ulses 

 coming from skin receptors. The proprio-ceptive field is 

 a sort of relay and supplement and extension of the field 

 of contact with the environment, or extero-ceptive field. 



A simile used by Sherrington helps us to understand the 

 import of this compounding of reflexes : "The receptor 

 system bears, therefore, to the efferent paths the relation 

 of the wide ingress of a funnel to the narrow egress. Fur- 

 ther, each receptor stands in connection not with one efferent 

 only but with many — perhaps with all — though as to some 

 of these only through synapses of high resistance. The 

 simile to a funnel will therefore be bettered by supposing 

 that within the general systemic funnel, of which the base 

 is five times wider than the egress, the conducting ])aths 

 from each receptor may be represented as a funnel Inverted 

 so that its wider end is more or less coextensive with the 

 whole plane of emergence of the final connnon patiis. This 

 gives some idea of the enormous formation of common 

 paths from tributary paths which must take ])lace.''' ^"^ 



And Sherrington forces home the truth of the scope o/ 

 the combinations by calling attention to the fact that under 

 strychnine poisoning "a muscle can be excited from prac- 

 tically any afferent nerve in the body." This is equiva- 

 lent to saying, he remarks, "that each final connnon ])ath is 

 in connection with jjractically each one of all the receptors 



