NORMAL AND ABNORMAL MOVEMENTS. 113 



To show how difficult it is to observe a moving limb, even 

 when the movement is slow, it need only be stated that medical 

 writers almost without exception describe this gait erroneously. 

 Almost all lay stress upon rigidity of the leg and insufficient 

 action of the knee-joint. It needs but a hasty examination of 

 the photographs to show how utterly wrong this view is. Every 

 one of the plates reveals the action of the knee-joint, and in 

 fact of all of the joints, to be far in excess of the normal ; and, 

 further, the rigidity is simulated and not real. Doubtless this 

 erroneous view has its origin in the difficulty of separating 

 mentally the active from the passive phase of the leg. Plate 

 550, which is one of the most instructive in the collection, ad- 

 mirably suits the purpose of an explanation. It is seen in study- 

 ing the upper lateral series that the passive leg, i.e., the one 

 suspended in the air, presents exaggerated knee-joint action 

 and that it at no time gives even the semblance of rigidity. The 

 moment, however, that it impinges on the ground, i.e., the mo- 

 ments it becomes active, all action at the knee ceases. More than 

 this, as the weight of the body is brought upon it, the extension 

 becomes absolute, and finally the knee is, so to speak, locked ; that 

 is, recurved. (This is well seen in No. 6 of the series,) By 

 means of this expedient the strain is thrown upon the bones and 

 ligaments of the joint rather than trusted to the treacherous 

 muscles. The rigidity is, therefore, not muscular, which, in fact, 

 all of our knowledge of ataxia forbids. How much voluntary 

 effort on the part of the muscles assists in steadying the limb, of 

 course depends upon the degree to which the disease has pro- 

 gressed. 



Regarding the action of the foot and the manner of its impact on 

 the ground various accounts have been given, some writers main- 

 taining that the heel strikes the ground first and considerably 

 in advance of the plantar surface, and others maintaining that the 

 entire sole strikes the ground at once. An examination of Plate 

 550 shows that the manner of impact probably depends upon the 

 degree of the ataxia. In the upper series, in which the patient 

 was photographed while having the guidance afforded by his eyes, 

 the heel impinges distinctly before the sole, while in the lower 

 series, in which the patient walked with closed eyes, the entire 

 plantar surface impinged at the same time. Occasionally the 



