1436 ON CUTANEOUS AND [BOOK in. 



coordination of movements. We have had occasion repeatedly to 

 insist that all the movements of the body, a large number of 

 those which are involuntary as well as all those which are 

 voluntary, are guided by afferent impulses, and that in the 

 absence of these afferent impulses the movements are apt to 

 become uncertain and imperfect, or even to fail altogether. We 

 need not here repeat what we have previously urged ; it is 

 sufficient for our present purpose to say that conspicuous among 

 these afferent impulses are those which form the groundwork of 

 the muscular sense ; at times they may do their work without 

 directly affecting consciousness but at other times they bring- 

 about a distinct affection of consciousness, and it is this affection 

 of consciousness which is more properly called the muscular 

 sense. 



Now, on the one hand, we find upon examination that co- 

 ordination of movements is not distinctly affected by the diminution 

 of cutaneous sensations, but may be maintained in the absence of 

 cutaneous sensations and indeed in the absence of the skin. Thus 

 frogs are said to be able to execute their ordinary movements 

 without signs of incoordination after the whole skin has been 

 removed. Cases of nervous diseases have been recorded in which, 

 if not complete absence of, at least great failure in, cutaneous 

 sensations has not been accompanied by any loss of coordination. 

 And if we appeal to our own consciousness we do not find the 

 muscular sense notably diminished by temporary anaesthesia of the 

 skin ; if, for instance, the skin of the arm be rendered for a while 

 anaesthetic, we do not find any marked change in our power of 

 judging weights or resistance, or in appreciating, with the eyes 

 shut, the position of the limb. 



On the other hand we find recorded cases of nervous diseases 

 in which loss of coordination, and loss of the muscular sense, as 

 indicated by the difficulty or inability to judge weights and 

 resistance and to recognize with the eyes shut the position of 

 the limbs or other parts of the body, have occurred without 

 notable loss of cutaneous sensations. This is often strikingly 

 shewn in cases of the disease or group of diseases known as 

 " tabes dorsalis," often spoken of from one of its prominent 

 symptoms as, " locomotor ataxy," the conspicuous pathological 

 condition of which is a structural change in the posterior columns 

 of the lower part of the cord. In certain stages of this disease the 

 patient may retain good cutaneous sensations, he may experience 

 tactile, temperature and painful sensations in the skin of his legs, 

 for instance, and possess adequate muscular strength in his legs, 

 and yet, from want of coordination, be unable to move them 

 properly unless he be assisted by sight. So long as his eyes are 

 open he may be able to stand and walk, but if his eyes are shut he 

 often falls, and when he moves, moves with a staggering uncertain 

 gait ; he fears, in the dark, to go up or down stairs even though 



