FATIGUE AND RECOVERY OF MUSCLES. 



497 



series exhibits a " staircase " character of its contractions just like the heart 

 ( 57).] 



[While an excised frog's muscle is fairly rapidly exhausted by single opening induction 

 shocks, at intervals of one second, human muscle in its normal relations may be almost in- 

 definitely so treated, and there is no change 

 in the record or any sensation of fatigue. 

 Waller regards this as favouring the view- 

 that the "fatigue consequent upon pro- 

 longed muscular exertion is normally cen- 

 tral rather than peripheral." Such results, 

 however, do not harmonise with those of 

 Zabludow r ski on the kneading of muscles, or 

 massage. Probably there are two factors, 

 one central, the other peripheral.] 



Blood Supply. If the arteries of a mam- 

 mal be ligatured, stimulation of the motor Fig. 343. 

 nerves produces complete fatigue after 120 Fatigue-curve of a frog's muscle. The sciatic nerve 

 to 240 contractions (in two to four minutes), was stimulated with maximal induction shocks 

 but direct muscular stimulation still causes an d every fifteenth contraction recorded (Stir- 

 the muscles to contract. In both cases the ling). 

 fatigue-curve is in the form of a straight 



line. If the blood supply to a mammalian muscle be normal, on stimulating the motor 

 nerve, the muscular contractions at first increase in height and then fall, their apices forming 

 a straight line (Rossbach and Harteneclc). In persons w-ho have used their muscles until fatigue 

 sets in, it is found that at the beginning the nerves and muscles react better to'galvanic and 

 faradic stimulation, but afterwards always to a less degree (OrschansJci). According to v. Kries, 

 a muscle tetanised and fatigued with maximal stimuli behaves like a fresh muscle tetanised 

 with sub-maximal stimuli ; both show an incomplete transition from the passive to the active 

 condition. 



[Relation of End-Plates. Muscle is fatigued far more rapidly than nerve, and the fatigue 

 begins in the muscle and not in the nerve, and it seems to be the weakest link in the chain 

 between nerve and muscle which is affected during excessive action, viz., the motor end-plate 

 ( Waller). In a nerve its conductivity is sooner affected by fatigue than its direct excitability. 

 Waller finds that after death " the excitability of a nerve persists when its action upon muscle 

 has ceased, such muscle being still excitable by direct stimulation." Some link in the chain is 

 obviously affected, and it is perhaps the end-plates.] 



[Action of Drugs on Fatigue. Waller finds, in a frog poisoned with veratrin, that if the 

 muscles be stimulated electrically, the characteristic elongation of the descent ( 298) gradually 

 disappears, but reappears 

 after a period of rest. In 

 this respect, strychnin in 

 its action on the spinal 

 cord behaves precisely 

 the same as veratrin on 

 muscle, viz., its effect is 

 dissipated by action and 

 restored by rest] Curara 

 and the ptomaines cause 

 an irregular course of the 

 fatigue-curve (Guareschi 

 andMosso). [If strychnin ' , , , . *? ' n , 



be injected into a frog Curves obtained by direct stimulation of the gastrocnemius of a frog 

 and the sciatic nerve on. poisoned with strychnin, the sciatic nerve divided on one side (upper 

 one side divided after the curve) and not on the other (lower or fatigue-curve), 

 strychnin tetanus has lasted for a time, the leg muscles of the side with the nerve undivided 

 exhibit signs of fatigue, as shown by direct stimulation of the muscles of both legs, when a 

 curve similar to fig. 344 is obtained. The higher one is the non-fatigued, the low T er that of the 

 side with the nerve undivided (Waller).] 



Recovery from the condition of fatigue is promoted by passing a constant electrical 

 current through the entire length of the muscle (Heidenhain), also by injecting 

 fresh arterial blood into its blood-vessel, or by very small doses of veratrin, [or 

 permanganate of potash], and by rest. 



If the muscle of an intact animal be stimulated continuously (fourteen days or so), until 

 complete fatigue occurs, the muscular fibres become granular and exhibit a wax-like degenera- 



2i 



