1062 ON CUTANEOUS AND [BOOK m. 



phenomena of incoordinate movements. In a previous part 

 of this work, we dwelt upon the importance of afferent 

 impulses as factors in the 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 pre- 

 viously 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 conscious- 

 ness, and it is this affection of consciousness which is more prop- 

 erly called the muscular sense. 



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

 coordination 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 decided loss of coordination. And if we appeal to our own 

 consciousness we do not find the muscular sense notably dimin- 

 ished 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 dis- 

 eases 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 col- 

 umns 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 muscu- 

 lar strength in his legs, and yet, from want of coordination, be 

 unable to move them properly unless he be assisted by sight. 



