96 



ANIMAL MECHANISM. 



becoming more and more abundant, invade the entire sub- 

 stance of the muscle. This phase of alteration, or fatty dege- 

 neration, is followed by an absorption of the substance of the 

 muscle, which disappears entirely at the end of a certain 

 time. 



Thus, not only does the volume of the organ increase or 

 diminish according as the necessities of its habitual function 

 require a greater or less force, but it wholly disappears when 

 its function is entirely suppressed. This effect is observed in 

 paralysis, where all nervous action is destroyed ; in certain 

 cases of dislocation, which bring closer together the two inser- 

 tions of a muscle, so as to render its action useless ; sometimes 

 even in fracture and anchyloses, which, by an abnormal con- 

 nection, render the two extremities of a muscle immovable, 

 and prevent any contraction of its fibres. 



But what will happen, if the muscle, instead of losing all 

 its function, only experiences a change with respect to the 

 extent of the movements which it can execute ? After certain 

 incomplete anchyloses, or certain dislocations, we see the 

 articulations lose more or less of their movements; as the 

 muscles which command flexion and extension only need, in 

 such cases, a part of the ordinary extent of their contraction. 



If the theory just enunciated be correct, these muscles ought 

 to lose a portion of their length. In order to verify this fact, 

 we have only to make a short excursion into the domain of 

 pathological anatomy. 



A warm discussion arose, sOme twenty years ago, as to the 

 transformation which the muscles underwent in those patients 

 who were afflicted with the deformity commonly known by the 

 name of club foot. Sometimes the foot is twisted upon the 

 leg, so that the surface which should be uppermost is next 

 the ground ; sometimes the foot is so forcibly extended that 

 the patient walks continually on its extremity. In all these 

 cases the muscles of the leg have only a very limited play ; 

 they undergo, therefore, either fatty or fibrous transformation. 

 Among these muscles, those which have no longer any action 

 undergo fatty degeneration, and then disappear ; while those 

 whose action is partly preserved, present only a change as to 

 the proportion of red fibre and tendon. In the latter case 



