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Mr. Graham Brown. 



variation of depth of narcosis. Thus it not rarely happens that, when the 

 depth of narcosis is certainly a constant one, the motor cortex becomes 

 suddenly inexcitable. This occurs, for instance, after a cortical discharge, 

 which is followed by " epileptic " after-discharge. But it also occurs without 

 any apparent preceding cause. Thus suddenly the cortical excitability 

 becomes abolished — at any rate, to practicable strengths of stimulation. 



This sudden loss of cortical excitability is a phenomenon of interest. It 

 is accompanied by two marked states. Of these, the first is an anaemia of 

 the cortex ; the second is a maintained postural contraction of certain of the 

 muscles of the limbs. The antenna seems to occur over the whole of the 

 small area of cortex — pre-central and post-central— usually exposed in these 

 experiments. It causes a sudden change in appearance from the " raw ham " 

 look of the cortex when it is in the most favourable condition for electrical 

 stimulation to a pale " dead " look. The cortex blanches ; it may be surmised 

 that it faints. 



The postural contraction of the muscles of the limb have most carefully 

 been examined in the case of the contralateral arm. In that member the 

 posture is one of flexion. The contraction of the flexors is a great one, and 

 it may be an exaggeration of the slight postural contractions (both flexion 

 and extension) which the arm always exhibits in changing degrees throughout 

 these experiments. But, from these muscular activities, this state of greater 

 contraction must be carefully distinguished. For, in the former, cortical 

 stimulation is effective, and can abolish or augment the postural contraction ; 

 but, in the latter case, the stimulation of the cortex is ineffective. 



When this curious phenomenon is examined, two points stand clearly out. 

 There occurs a postural activity of the flexor muscles of the contralateral 

 arm, and this is accompanied by anaemia and by inexcitability of the cortex. 

 The similar state of inexcitability which is seen after post-stimulatory 

 cortical epilepsy is also accompanied by blanching of the cortex, and often 

 by maintained posture of the arm. 



From these facts the conclusion may be drawn that the postural activity of 

 the limbs in this state is conditioned by the activity of certain of the lower 

 centres. The question arises — which are these ? 



II. Methods Employed. 



The animals used in the present experiments were small monkeys : Macacus rhesus, 

 Macacus sinicus, Callothrix, Cercocebiis cethiops. They were kept unconscious throughout 

 the whole experiment, and until they were destroyed at its conclusion. The procedures 

 of decerebration, removal of the cerebellum, etc., were performed in the usual manners. 



Stimulation of the varioiis parts of the neuraxis was performed in the unipolar method. 

 Two unipolar electrodes were used in order that two points might be simultaneously 



