632 



Professor Jagadis Chunder Bose 



[May 10, 



invariably after a definite period of stimulation. In tin, at least, 

 Guccessive tetanic curves are almost exactly similar. The maximum 

 effect depends on the intensity of the stimulus (Fig. 12). 



Amongst living substances we find nerve prac- 

 Fatigue. tically indefatigable. Successive curves are ex- 



actly similar. But with muscle there is a rapid 

 decline in the responses (Fig. 4). Fatigue, however, disappears 

 after a period of rest. 

 It is generally sup- 

 posed to be due to 

 the working of two 

 processes conjointly 

 — the breakdown of 

 force-producing ma- 

 terial and the accum- 

 ulation of " fatigue- 

 stuffs." It is thought 

 that fatigue is re- 

 moved by the action 

 of the circulating 

 blood in bringing in 

 fresh material and 

 carrying away fa- 

 tigue products. But 

 that this cannot 

 furnish a complete 

 explanation of the 

 phenomena is shown by the fact that excised bloodless muscle acted 

 on by stimulus, recovers from fatigue after a short period of rest, 



though here there is no blood- 

 supply to repair the damage and 

 remove the waste products. 



Turning to inorganic sub- 

 stances, we find different metals 

 exhibiting fatigue. But tin ex- 

 hibits very little, reminding us in 

 this of the behaviour of nerves. 

 Even here, however, after pro- 

 longed action, fatigue is sometimes 

 observed. The fatigue curve here 

 reproduced was obtained from tin 

 that had been acted on for several 

 days, and its remarkable similarity 

 to the curve of fatigue in muscles 

 will be at once apparent (see Figs. 

 13 and 4). That fatigue is pri- 

 marily due to over-strain, and not to fatigue products, is seen from the 

 fact that a brief period of repose hastens its removal in this case also. 



Fig. 12. — Tetanic curves in tin, showing effects of 

 different intensities of stimuli. The three curves to 

 the left show effect of vibration with amplitude of 90° ; 

 the next three are due to stronger intensity of stimulus, 

 amplitude = 180°; the amplitude was now reduced to 

 90°, and the last two, owing to fatigue, show feebler 

 response than the first three. 



Fig. 13. — Photographic record of 

 fatigue in tin (compare with Fig. 4). 



