DIMINISHED IRRITABILITY; DEATH OF THE NERVE. 633 



The motor nerve possesses a greater specific irritability to electrical stimuli 

 than the muscle-substance. This can be recognized from the circumstance that 

 contractions take place on feebler stimulation if the nerve rather than the curarized 

 muscle is stimulated. 



Mention should yet be made of the remarkable fact that on irritation of a 

 motor nerve the stimulating effect (contraction) is under certain circumstances 

 the greater the nearer the point of stimulation to the central nervous system. 

 According to v. Fleischl, however, the nerves are equally responsive to chemical 

 stimuli at all points in their course. For electrical stimuli they are more responsive 

 in their proximal portions only when the stimulating current is of the descending 

 type. The reverse is said to be the case when the current is of the ascending 

 type. Rutherford and Hallsten found that the reflex contractions induced by the 

 irritation of a sensory nerve are the greater the more proximally the irritation is 

 applied. 



Nerve-fibers of like function in the same trunk do not always have the same 

 degree of irritability. Thus, for example, feeble stimulation of the sciatic nerve 

 of the frog causes contractions only of the flexors, while stronger stimulation is 

 required to induce contraction also of the extensors. The effects of stimulation 

 with long or with short intervals are analogous. According to Ritter, the nerves 

 for the flexors also degenerate first. In a similar manner feeble stimulation of 

 the hypoglossal nerve causes retraction of the tongue, while strong stimulation 

 causes protrusion. In the facial nerve the fibers for the eyelids are more irritable 

 than those for the mouth or the ear. 



Also on direct irritation of the muscles (of curarized animals) the flexors 

 contract in response to a weaker current than the extensors, but at the same time 

 the former are more readily exhausted. Poisons generally injure the flexors 

 earlier than the extensors. Treatment of a frog-preparation with ether causes 

 flexion to occur on strong stimulation of the sciatic nerve. Increase of the stimu- 

 lation, however, finally causes extension. Likewise, strong stimulation of the 

 recurrent, laryngeal nerve during deep ether-narcosis causes dilatation, during 

 slight intoxication constriction, of the glottis. Dilatation of the glottis has been 

 induced by feeble stimulation. The adductor muscle of the crab's claw relaxes 

 on feeble stimulation, while it undergoes contraction on strong stimulation. 



Stimuli may be applied also by means of a single electrode of the induction - 

 apparatus unipolar induced effect. The cause resides in a movement of the 

 electrical fluid to and from the free extremities of the open induced circuit at the 

 moment of induction. 



Upon muscles the action of electrical irritants is entirely similar to that upon 

 nerves. The following, however, is noteworthy: currents of short duration have 

 no effect upon muscles whose nerves are paralyzed by curare, as well as .upon 

 muscles enfeebled by intense exhaustion, degeneration, or pathological paralytic 

 conditions. 



A remarkable reaction designated galvanotropism is exhibited by entire animals 

 when a current is passed through them. Feeble currents cause the animal to 

 be thrown into a position with its long axis corresponding to the direction of the 

 current, while strong currents have the opposite effect. 



DIMINISHED IRRITABILITY; DEATH OF THE NERVE. 

 NERVE-DEGENERATION AND NERVE-REGENERATION. 



The persistence of normal irritability in a nerve within the intact 

 body depends first upon normal nutritive processes and the blood-supply 

 of the nerve. In this relation it should be especially mentioned that 

 insufficient nutrition is generally followed at first by an increase in the 

 irritability. Only after advanced disturbance does the irritability 

 diminish. 



The physician should constantly bear in mind that whenever he encounters 

 evidences of increased irritability of nerves under the influence of defective or 

 disturbed nutrition, as may be manifested in various ways-, such as general ner- 

 vousness and irritable weakness, etc., the condition is the beginning stage of a 

 diminution of nerve-energy. Under such circumstances the nutrition should be 



