i GENEEAL PHYSIOLOGY OF MUSCLE 35 



of the nervous system, some of which may also be produced 

 artificially in healthy subjects, and by certain poisons which act 

 directly upon muscle. 



It should be added that muscle tone may be inhibited under 

 special conditions ; i.e. it may suffer a negative variation in which 

 the length of the muscle is exaggerated beyond the normal. 



An interesting example of obvious lengthening of the muscles 

 after direct excitation of their motor nerves was first observed by 

 Kichet (1882) on the muscles of the crab's claw. This organ for 

 the capture of prey and weapon of offence and defence consists of 

 two arms, one of which is fixed, the other movable by means of 

 two muscles of antagonist action, the one a very delicate abductor, 

 the other a much thicker and stronger adductor. If the rigid 

 branch of the claw be fixed in a clamp, and a thread attached to 

 the movable arm, it is easy (either by direct transmission to a 

 writing-lever, or by indirect transmission through a couple of 

 Marey's tambours joined together) to record on a moving drum 

 the reactions of the claw-muscles to induced or constant currents, 

 acting directly on the nerves of the claw, or on one or other of the 

 muscles. 



On exciting the nerve with a weak current, Eichet saw that 

 the claw opened; on exciting with a strong current, on the 

 contrary, it closed. In the first case the action of the abductor 

 prevailed, in the second, of the adductor. 



Eichet's observation was confirmed by Luchsinger, and 

 elucidated by further experiments of Biedermann (1887-88). If 

 the abductor is divided before exciting the nerve of the claw, the 

 result is the same as in Eichet's experiments ; with weak stimula- 

 tion the claw opens, with stronger excitation it closes. In the 

 first case, therefore, there is elongation or relaxation of the adductor, 

 in the second, contraction. If, on the contrary, the adductor be 

 cut, a weak current causes opening of the claw, or contraction of 

 the abductor, a stronger current closing of the claw and lengthen- 

 ing of the muscle. The elongation of the muscle apparent in the 

 first experiment with weak stimulation, in the second with strong, 

 was interpreted by Biedermann as an inhibition of muscle tone, 

 similar to that produced in cardiac muscle by excitation of the 

 vagus. 



Piotrowski (1893) confirmed the fact already noted by Bieder- 

 mann that to produce the inhibitory effect it is essential that the 

 preparation should be in a state of considerable tonic excitation ; 

 in fact it can never be obtained in summer, when the tone of the 

 muscles is low. He noted further that the same current may 

 evoke now contraction and now inhibition, according as the tone 

 of the preparation is low or high. Temperature has a marked 

 effect on the phenomenon ; high temperatures abolish the 

 inhibitory effect ; low temperatures favour it ; the optimum for 



