578 REACTION OF DEGENERATION. 



time, or one on the head and the other on a point as near as possible to the supposed seat of 

 the lesion. The current must not be too strong nor applied too long. 



Induced v. Constant Current: Eeaction of Degeneration. Paralysed nerves and muscles 

 behave quite differently as regards the induced (rapidly interrupted) and the constant current. 

 This is called the "reaction of degeneration." We must remember the physiological fact that 

 a dying nerve attached to a muscle ( 325), and also the muscles of a curarised animal, react 

 much less strongly to rapidly interrupted currents than fresh non-curarised muscles. Baierlacher, 

 in 1859, found that, in a case of facial paralysis, the facial muscles contracted but feebly to the 

 induced current, but very energetically on the constant current being used. The excitability 

 for the constant current may be abnormally increased, but may disappear on recovery taking 

 place. According to Neumann, it is the longer duration of the constant current as opposed to 

 the momentary closing and opening of the induced current which makes the contraction of the 

 muscle possible. If the constant current be broken as rapidly as the Faradic current is broken, 

 then the constant current does not cause contraction. Conversely, the induced current may be 

 rendered effective by causing it to last longer. We may also keep the primary circuit of the 

 induction machine closed, and move the secondary spiral to and fro along the slots. Thus we 

 obtain slow gradations of the induced current which act energetically upon curarised muscles 

 [BrUcke). Hence, in stimulating a muscle or nerve, we have to consider not only the strength, 

 but also the duration, of the current, just as the deflection of the magnetic needle depends upon 

 these two factors. 



[Galvanic excitability is the term applied to the condition of a nerve or muscle, whereby it 

 responds to the opening or closing of a continuous current. The effects differ according as the 

 current is opened or closed, and according to its strength. As a rule, the cathode causes a con- 

 traction chiefly at closure, the anode at opening the current, while the cathode is the stronger 

 stimulus. With a weak current, the cathode produces a simple contraction on closing the current, 

 but no contraction from the anode. With a medium current, we get with the cathode a strong 

 closing contraction but no opening contraction, while the anode excites feeble opening and 

 closing contractions. With a strong current, we get with the cathode a tetanic contraction at 

 closure, and a perceptible contraction at opening, while with the anode there is contraction both 

 at opening and closing.] 



[The law of contraction is usually expressed by the following formula (Erb) : An = anode, 

 Ca = cathode, C = contraction, c = feeble contraction, C' = strong contraction, S = closure of 

 current, = opening of current, Te = tetanic contraction so that, expressing the above state- 

 ments briefly, we have 



Weak currents produce Ca S C ; 



Medium ,, ,, Ca S C, An S c, An c ; 



Strong ,, CaSTe, An S C, An C. CaOc] 



[Typical Reaction of Degeneration. When the reaction of the nerve and muscle 

 to electrical stimulation is altered both qualitatively and quantitatively, we have 

 the reaction of degeneration, which is characterised essentially by the following 

 conditions] : The excitability of the muscles is diminished or abolished for the 

 Faradic current, while it is increased for the galvanic current from the 3rd to 58th 

 day ; it again diminishes, however, with variations, from the 72nd to 80th day ; the 

 anode closing contraction is stronger than the cathode closing contraction. The con- 

 tractions in the affected muscles occur slowly in a peristaltic manner, and are local, 

 in contrast with the rapid contraction of normal muscle. The diminution of the 

 excitability of the nerves is similar for the galvanic and Faradic currents. If the 

 reaction of the nerves be normal, while the muscle during direct stimulation with 

 the constant current exhibits the reaction of degeneration, we speak of " partial 

 reaction of degeneration," which is constantly present in progressive muscular 

 atrophy (Erb). 



[The ''reaction of degeneration" may occur before there is actual paralysis, as in lead 

 poisoning. When it occurs we have to deal with some affection of the nerve-fibres, or of the 

 trophic nerve-cells. When it is established, (1) stimulation of the nerve with Faradic and 

 galvanic electricity does not cause contraction of the muscle ; (2) direct Faradic stimulation of 

 the muscles does not cause contraction ; (3) the galvanic current usually excites contraction 

 more readily than in a normal muscle, so that the muscle responds to much feebler currents 

 than act on healthy muscles, but the contraction is longer and more of a tonic character, and 

 shows a tendency to become tetanic. The electrical excitability is generally unaffected in 

 paralysis of cerebral origin, and in some forms of spinal paralysis, as primary lateral sclerosis 

 and transverse myelitis, but the " reaction of degeneration " occurs in traumatic paralysis, due 

 to injury of the nerve-trunks, neuritis, rheumatic facial paralvsis, lead palsy, and in affections 



