i GENERAL PHYSIOLOGY OF MUSCLE 31 



muscle and the stretching to which it is mechanically subjected. 

 One advantage of this extension is that, even if fully relaxed, the 

 muscle on contraction immediately approximates its two points 

 of insertion, without any loss through mechanical causes. 



The elastic tension of the resting muscle under normal con- 

 ditions is not, however, explained solely by this passive traction. 

 During life it undergoes marked oscillations under various 

 conditions. This tension of the muscle, which is not passively 

 determined by the distance between its points of insertion but 

 is the expression of muscular activity, is known as its tone. 



Many facts show that the natural length of the resting 

 muscle, on which its natural tone depends, is directly dependent 

 on the nervous system. We shall elsewhere study the mechanism 

 of this constant tonic influence which the nerve exercises upon 

 the muscle : here we must confine ourselves to describing the 

 classical experiment of Brondgeest (1860) which demonstrates it. 

 If the lumbar plexus of a frog is cut on one side, after its spinal 

 cord has been divided higher up so as to paralyse voluntary 

 movements, and the animal is suspended vertically by its head, 

 the two hind-limbs of the animal take up essentially different 

 positions. The leg of the side on which the nerves were cut 

 hangs fully extended, i.e. the muscles are flaccid, while that of 

 the other side, on which the nerves are intact, is slightly flexed 

 owing to the tone of the muscles. A similar phenomenon is 

 observed on man in the fairly frequent cases of facial paralysis ; 

 the distortion of the mouth and nose, which is very pronounced 

 in speaking, is also obvious even in the state of absolute inactivity 

 of all the facial muscles ; it is due to loss of tone in the muscles 

 of the paralysed side and its persistence in the muscles of the 

 sound side, owing to which the latter pull on the former. 



In certain abnormal conditions of the ne'rvous system as in 

 hysteria, somnambulism, and hemiplegia of long standing the 

 tone of the muscles may be enormously exaggerated and become 

 contractured (Brissaud and Richet). This condition is essentially 

 different from tetanus, which is due, as we have seen, to summation 

 and fusion of muscular contraction. Simple twitches and even 

 a true tetanus can be obtained from contractured muscles, by 

 suitable electrical stimulation, as in the normal resting muscle ; 

 and the characteristic muscle sound can be heard during tetanus, 

 that is absent in simple contracture (Brissaud and Boudet). 



Independently, again, of the nervous system, contracture may 

 result from intrinsic alterations in the muscle, caused by certain 

 poisons. This is a tonic state, quite distinct from the rapid 

 contractions which can also be evoked from the muscle by means 

 of make or break shocks during contracture. Among the poisons 

 capable of producing this phenomenon, veratrin has been the 

 most studied, particularly by von Bezold, Fick, Bohm, and others. 



