THE MUSCULAR SYSTEM. 263 



but very capable of producing great effects, when the states of contrac- 

 tion and of rest are duly alternated, as for instance in walking, running, 

 &c., and in the heart and respiratory muscles. 



The importance of this view of the nature of the muscular "tone," 

 as regards the physiology of the nerves, is sufficiently obvious ; but in 

 pathology also, it may be employed, in explanation of the retraction of 

 divided muscles, and the shortening which takes place in muscles whose 

 antagonists are paralyzed. The former, as correctly pointed out by E. 

 "Weber, depends upon the elastic force, and takes place, as far as I know, 

 only in extended, tense muscles, but not in those which are in a state of 

 contraction, which, on the contrary, when cut across, immediately be- 

 come lengthened, as may be readily observed in the Frog. It is quite 

 true, that contractions also take place in divided muscles, in conse- 

 quence of nervous influence ; but these are never more than local, and 

 cease without the production of any important effect on the form of the 

 wound in the muscle. 



The shortening which occurs in the antagonists of paralyzed muscles, 

 is not referable either to the elastic force of the non-paralyzed muscles, 

 which is much too slight to influence the position of a limb, or to their 

 persistent "tone," but depends simply upon the voluntary innervation 

 of the muscles, which are still in an active condition, and which, no 

 longer meeting with any opposition from their antagonists, draw the limb 

 in their own direction. The persistence of the oblique position which 

 now ensues, may be readily explained without our necessarily assuming 

 the existence of a permanent contraction, when it is considered that 

 muscles, the antagonists of which are paralyzed, never again become 

 elastically tense. In lead-palsy, for instance, when the first contraction 

 of the flexors, consequent upon the paralysis of the extensors, ceases, 

 the former, even under the most favorable circumstances, become ex- 

 tended only so far as to assume their natural form, a condition from 

 which necessarily results the semiflexed position of the part affected. 

 In accordance with this view, I regard the permanent condition of the 

 unaffected side of the face, in one-sided paralysis of the facial nerve, and 

 that of the upper eyelids in blepharoptosis, as produced, not by a per- 

 sistent contraction, but as indicative of a state of perfect rest in the 

 muscles, except when voluntary movements take place. The falling of 

 the upper eyelid is explained by the paralysis of the levator, and the 

 inability of the orbicularis, by its extension after a previous closure, to 

 raise the eyelid beyond a certain point. In the same way the distortion 

 of the face is produced, at first by the voluntary contraction consequent 

 on the paralysis, upon the cessation of which it is impossible that the 

 previous symmetry of the features should be restored, because the anta- 

 gonist muscles on the opposite side are paralyzed, and their slight elastic 

 force during life is insufficient, simply upon the cessation of the contrac- 



