312 Mr. Graham Brown. Intrinsic Factors in the [July 21, 



de-afferented hind limb of the cat may be made to scratch. Although this is 

 perhaps not conclusive — in view of the possible influence of stimuli which 

 arise in the opposite hind limb — he and the present author have recently 

 demonstrated at a meeting of the Physiological Society a cat in which 

 scratching may be elicited although both hind limbs have been completely 

 de-afferented. 



The phasic alternation of maintained flexion in the scratching phenomenon 

 of the guinea-pig under anaesthesia in many ways resembles the phasic 

 alternation of flexion in the act of progression, and has suggested for some 

 time to the present author that the act of progression may, too, be essentially 

 a central and not a peripheral phenomenon. 



II. Operative Procedure. 



In these experiments the animal used was the decerebrate cat, and the 

 movements of the isolated tibialis antieus and gastrocnemius were recorded. 

 Before decerebration a loose ligature was placed round the spinal cord at the 

 level of the 11th, 12th, or 13th pair of thoracic spinal roots; and all the 

 posterior spinal roots caudal to, and including, the 6th lumbar root were 

 divided upon the side of the recording muscles. In the limb of that side all 

 the other muscles were put out of action by the severance of their motor 

 nerves or of their substance ; there remained in action only the muscles 

 supplied by the branches of the popliteal nerves in the leg, and these, besides- 

 having their tendons cut, were de-afferented by the section of the lumbar roots. 

 The long saphenus nerve, a purely afferent one, was left intact for another 

 purpose. In the opposite hind limb all the muscles were de-afferented by 

 the section of their nerves or by the section of their substance ; there remained 

 of the nerves of that limb only the long saphenus nerve. 



In effect this procedure completely de-afferented the two hind limbs, 

 including the muscles whose movements were to be recorded. 



To record the muscular movements the leg was firmly fixed in steel clamps r 

 and the recording muscles wrote upon the myograph by means of light 

 aluminium levers to which their tendons were attached by threads. 



An interval of about five hours was allowed to elapse between the 

 end of the operative procedure described above and the experiment about to 

 be described. 



It is hardly necessary to state that up to the time of decerebration the 

 animal was kept completely under the influence of the anaesthetic. 



