188 ELECTROTONUS [GIL XVI. 



When the motor nerve is degenerated, and will not respond to 

 any form of electrical stimulation, the muscle also loses all its power 

 of response to induction shocks. The nerve-degeneration is accom- 

 panied by changes in the nutrition of the muscular fibres, as is 

 evidenced by their rapid wasting, and any power of response to 

 faradism they possessed in the normal state is lost. But the response 

 to the constant current remains, and is indeed more ready than in 

 health, doubtless in consequence of nutritive changes which develop 

 what the older pathologists called, truly enough, " irritable weakness." 

 There is, moreover, a qualitative as well as a quantitative change. 

 In health the first contraction to occur on gradually increasing the 

 strength of the current is at the negative pole, when the circuit is 

 closed (see Pfluger's law), and a stronger current is required before 

 closure-contraction occurs at the positive pole. But in the morbid 

 state we are discussing, closure -con traction may occur at the positive 

 pole as readily as at the negative pole. This condition is called 

 the " Reaction of Degeneration." 



Suppose a patient comes before one with muscular paralysis. 

 This may be due to disease of the nerves, of the cells of the spinal 

 cord, or of the brain. If the paralysis is due to brain disease, the 

 muscles will be slightly wasted owing to disuse, but the electrical 

 irritability of the muscles and nerves will be normal, as they are 

 still in connection with the nerve-cells of the spinal cord that control 

 their nutrition. But if the paralysis is due to disease either of the 

 spinal cord or of the nerves, this nutritive influence can no longer 

 be exercised over the nerves or muscles. The nerves will degenerate ; 

 the muscles waste rapidly; the irritability of the nerves to both 

 forms of electrical stimulation will be lost; the muscles will not 

 respond to the faradic current, but in relation to the constant current 

 they will exhibit what we have called the " reaction of degeneration." 



This illustrates the value of the electrical method as a means of 

 diagnosis, that is, of finding out what is the matter with a patient. 

 It is also a valuable means of treatment ; by making the muscles con- 

 tract artificially, their nutrition is kept up until restoration of the 

 nerves or nerve-centres is brought about. Another illustration will 

 indicate that the facts regarding electrotonic variation of excitability 

 are true for sensory as well as for motor nerves; in a case of 

 neuralgia, relief will often be obtained by passing a constant current 

 through the nerve ; but the pole applied to the nerve must be the 

 anode which produces diminution of excitability, not the kathode 

 which produces the reverse. 



Waller has pointed out that Pfluger's law of contraction, as formulated for 

 frogs' muscles and nerves, is true for human muscles and nerves in the main, but 

 there are certain discrepancies. These arise from the method necessarily employed 

 in man being different from those used with a muscle-nerve preparation. In a 

 muscle-nerve preparation the nerve is dissected out, the two electrodes placed on 



