CENTRAL OHGAN AND PEEIPHEEAL NERVES (PHYSIOLOGICAL). 43 



papillffi and the tactile papillas. Good staining discloses with each of them 

 plexuses of unsuspected density of arborization. 



For what services may such an abundant sensory innervation be pro- 

 vided? It occurs immediately to one that there is a great number of re- 

 flexes, very necessary to the preservation of the individual, even though he 

 be unaware of them. The regulation of the secretions, the blood-supply 

 to the skin in relation to the caloric body-economy of the organism, the 

 adjustment to varying illumination, the tension of the muscles and tendons 

 through the respective tendon-reflexes, the different response by such vary- 

 ing tensions according to the intensity of the voluntary impulse, and many 

 other phenomena could be cited. To all of them is necessary, besides the 

 motor part of the reflex-arc, a sensory part. Indeed, Exner, to whom we are 

 indebted for indicating the importance of these short reflex-arcs and the 

 rSles they play in the organism, has pointed out how, in general, for the 

 production of any movement the sensory innervation must be intact. The 

 act of swallowing, for example, divides into a voluntary and a reflex act. 

 Ansesthetize the pharynx with cocaine, and the ability to perform the volun- 

 tary part of swallowing is preserved; the bolus, however, on reaching the 

 oesophagus, produces no impression on it, and the reflex part of the act is 

 lost. Here, then, is the reason why the mucous membrane of the gullet 

 possesses such an apparently superfluous sensory innervation, arid why, be- 

 neath and in its epithelium, there lie such great plexuses of nerve-fibers. 

 Another good example of the importance of sensory regulation of purely 

 motor phenomena is offered by the movements of the fingers. These move- 

 ments are much impaired — the "fingers are stiff" — when sensory dis- 

 turbances alone are present in the hand. This can be brought about arti- 

 ficially. Let the hand become too cold, and it becomes stiff; i.e., cannot 

 move well, even in those movements depending upon the muscles lying in 

 the protected forearm. These latter muscles cannot contract normally, it 

 appears, when no regulating impressions arrive from the tendon and joint 

 nerve-endings. The stiff fingers, which one experiences often on a winter's 

 walk, are due to the presence of " Senso-mobility." Probably many motor 

 disturbances of hysteria are of this category. 



An abundant sensory innervation is, therefore, necessary, not only for 

 countless reflex actions, but for the regulation of many seemingly purely 

 voluntary movements, as well. 



By "sensory innervation," however, one must not think only those proc- 

 esses are meant which enter into our consciousness, but rather all those by 

 which from any place in the body impressions are conducted to the nearest 

 ganglion or to the central axis. Whether they be conducted farther still, 

 or whether they be recognized by the individual as they occur, does not 

 affect their nature. Sensation and perception are not the same thing. 



