CHAP, vi.] THE BRAIN. 633 



influence of narcotic drugs such as morphia. In certain stages of 

 narcotism by morphia, the dose required varying according to the 

 individual, but generally being large, the irritability of the cortex 

 is diminished ; currents which previously readily produced contrac- 

 tions in the muscles corresponding to the area stimulated, now 

 produce little or none at all ; and indeed the cortex may be thus 

 brought to such a condition that even very strong currents produce 

 no movements at all. In such cases, movements may, at times at all 

 events, be brought about by removing the cortex and applying the 

 electrodes directly to the underlying white matter, thus shewing 

 that the morphia produces its effects, in part at least, by acting 

 directly on the cortex itself. From this we gain an additional ar- 

 gument in favour of the independent irritability of the cortex. 



On the other hand in certain stages of the action of morphia 

 the irritability of the cortex is not diminished, but on the contrary 

 increased. It is well known that an animal under the influence of 

 morphia frequently manifests an increase of reflex excitability, 

 being for instance remarkably sensitive, and readily responding to 

 the stimuli of sounds and noises ; and a similar exaltation has been 

 observed in reference to the influence of electric stimuli applied to 

 the cortical areas. At times this increased excitability may become 

 so developed that the application of even a moderate stimulus 

 leads to epileptiform convulsions lasting for some considerable 

 time. Not unfrequently indeed, experiments of this kind have 

 to be suspended on account of the appearance of these convulsions. 

 When any particular 'motor area' is being stimulated the con- 

 vulsive contractions generally appear first in the appropriate group 

 of muscles and thence spread first over the same side and then over 

 the- other side of the body until sometimes the whole frame is 

 convulsed. When the cortex is removed, and the electrodes are 

 applied directly to the subcortical white matter, these convulsions 

 are not nearly so readily produced, and when they appear are not 

 exactly of the same character, being generally limited to one side of 

 the body. It would thus appear that the convulsions, though carried 

 out by the nervous machinery of the lower parts of the brain and 

 more especially perhaps by the so-called 'convulsive centre' in the 

 medulla oblongata, originate and to a large extent are fashioned by 

 changes in the cerebral cortex ; and, though this is a matter into 

 which we must not go more fully here, pathological and clinical 

 observations similarly tend to shew that epilepsy itself, in certain 

 cases at all events, is the product of an abnormal action of the 

 cerebral convolutions. 



From what has been said in previous sections, more particularly 

 in reference to the reflex actions of the spinal cord (p. 592) and co- 

 ordinating mechanisms (p. 619), the reader will be prepared for the 

 observation that the phenomena of these convulsions suggest the 

 idea that they arise not so much from a positive increase in the 

 explosive, discharging energy of the central nervous mechanisms as 



