UNIPOLAR STIMULATION AND NORMAL NUTRITION. 537 



Direct stimulation of the muscles in curarised animals shows that the flexors contract with a 

 feebler stimulus (but also fatigue sooner) than the extensors ; the pale muscles of the rabbit are 

 also more excitable than the red. As a rule, poisons affect the flexors sooner than the extensors. 

 In some muscles some pale fibres are present, and they are more excitable than the red 

 (Grutzner) ( 298). If a frog's nerve-muscle preparation be exposed to the action of ether, 

 on strong stimulation of the sciatic nerve, flexion occurs (Gr-iitzner, Boxcditch), but, if the current 

 be made stronger, extension takes place. During deep ether-narcosis, strong stimulation of the 

 recurrent nerve causes dilatation, and with slight narcosis, narrowing of the glottis takes 

 place ; dilatation occurs on slight stimulation (Bovjditch). The adductor muscle of the claw of a 

 crayfish is relaxed under a weak stimulus, but it contracts when a strong stimulus is applied 

 to it. The reverse is the case with the muscle which opens the claw (Biedermann). 



Unipolar Stimulation. If one electrode of an induction apparatus be applied 

 to a nerve, it may act as a stimulus. Du Bois-Reymond has called this " unipolar 

 induction action." It is due to the movement of the electrical current to and from 

 the free ends of the open induction current at the moment of induction. [Unipolar 

 induction is more apt to occur with the opening than the closing shock, because 

 the former is more intense.] 



Upon muscle, electrical stimuli act quite as they do upon nerves. Electrical 

 currents of very short duration have no effect upon muscles whose nerves are 

 paralysed by curara (Brilcke), and the same is true of greatly fatigued muscles, or 

 muscles about to die or greatly weakened by diseased conditions ( 399). 



325. DIMINUTION OF THE EXCITABILITY DEGENERATION AND 

 REGENERATION OF NERVES. 1. Normal Nutrition. The continuance of 

 the normal excitability in the nerves of the body depends upon the maintenance of 

 the normal nutrition of the nerves themselves and a due supply of blood. Insuffi- 

 cient nutrition causes, in the first instance, increased excitability, and if the condi- 

 tion be continued the excitability is diminished ( 339, I.). 



When the physician meets with the signs of increased excitability of the nerves, under bad or 

 abnormal conditions of nutrition, this is to be regarded as the beginning of the stage of decrease 

 of the nerve-energy. Invigorating measures are required. 



If the terminal nervous apparatus be subjected to a temporary disturbance of its 

 nutrition, the return of the normal nutritive process is heralded by a more or less 

 marked stage of excitement. The more excitable the nervous apparatus, the 

 shorter must be the duration of the disturbance of nutrition, e.g., cutting off the 

 arterial blood supply or interfering with the respiration. 



2. Fatigue. Continued excessive stimulation of a nerve, without sufficient 

 intervals of repose, causes fatigue of the nerve, and by exhaustion rapidly 

 diminishes the excitability. A nerve is more slowly fatigued than a muscle 

 (Bernstein), but it recovers more slowly ( 304). [Nerves of cold-blooded animals 

 ( Widenskii) and mammals (Bowditch) may be tetanised for hours without becoming 

 fatigued.] 



[To show that a muscle is much more rapidly fatigued than a nerve, Bernstein arranged two 

 nerve-muscle preparations so that both nerves were tetanised simultaneously, but through one of 

 the nerves, a polarising constant current was passed by means of non-polarisable electrodes ( 327), 

 so that the condition of anelectro tonus ( 335) was set up in this nerve, and thus "blocked" 

 the propagation of impulses to the corresponding muscle. Only one muscle, therefore, was 

 tetanised. Both nerves were continuously stimulated until fatigue of the contracting muscle 

 took place, and on breaking the polarising current applied to the other nerve, the corresponding 

 muscle at once became tetanic. Now, as both nerves were equally stimulated, and the muscle 

 in connection with one nerve was fatigued, while the other muscle at once contracted, it is 

 evident that a muscle is much more rapidly fatigued than a motor nerve. In sensory nerves, 

 fatigue and recovery are analogous to the corresponding processes in motor nerves (Bernstein).'] 



Recovery. When a nerve recovers, at first it does so slowly, then more rapidly, 

 and afterwards again more slowly. If recovery does not occur within half an hour 

 after a frog's nerve has been subjected to very long and intense stimulation, it will 

 not take place at all. 



