FUNCTIONS OF THE BRAIN 943 



in the well-known fact that the large pyramidal cells whose axons form 

 the pyramidal tract make up but a small proportion of the total number 

 of pyramidal cells in this region, which, besides, contains numerous cells 

 of Golgi's second type (p. 828). And although it may be true that the 

 tactile sensations constituting the so-called body-sense are represented 

 mainly not in the motor region itself, but in the adjacent gyrus post- 

 centralis posterior, to the Rolandic fissure (p. 918), there is nothing to 

 contradict the supposition that the discharge of energy from the most 

 circumscribed motor area or element may be accompanied with con- 

 sciousness. And, indeed, some writers have supposed that such a 

 consciousness of, or even conscious measurement of, the discharge 

 from the ' motor ' areas is the basis of the muscular sense (Bain, 

 Wundt). 



So far, at least, as the ' motor ' region and the grey matter imme- 

 diately around the neural canal are concerned, the analogy of an 

 electrical switch-board connected with machines of various kinds might 

 be more correct. Touch one key or another, and an engine is set in 

 motion to grind corn, or to saw wood, or to light a town. The difference 

 in result lies not in any difference of material or workmanship in the 

 switches, but solely in the difference in their connections. 



Grey matter in the upper part of the precentral convolution is excited, 

 and the muscles of the leg contract. Grey matter on the lower part of 

 the convolution is excited, and there are movements of the face and 

 mouth. Grey matter in the medulla oblongata is excited, and the 

 salivary glands pour forth a thin, watery fluid, poor in proteins, and 

 containing an amylolytic ferment. Another portion of grey (?) matter 

 in the medulla is thrown into activity, and the pancreatic ducts 

 become flushed with a thicker secretion, relatively rich in proteins and in 

 ferments which act on proteins, starch, and fat. Here, too, there is a 

 variety in result according as one or another nervous switch is closed ; 

 here, too, the variety is due, not to essential differences in the structure 

 of the activity or the nervous centres, but to their connection, by nervous 

 paths, with peripheral organs of different kinds. There is, indeed, a 

 specialization, a localization, of function, but the localization is at the 

 periphery, the specialization is in the peripheral organs. 



It may be asked whether, if this is the case for the peripheral organs 

 of efferent nerves, the converse does not hold true for the afferent nerves 

 in other words, whether the localization here is not at the centre. And 

 that there is in some degree a central localization of sensation may be 

 considered proved by the well-known clinical fact, already referred to, 

 that sensations of various kinds may be produced by pathological 

 changes in the cortex. For example, a tumour involving the upper part 

 of the temporal lobe may give rise to epileptiform convulsions preceded 

 by an auditory aura, a sound, it may be, resembling the ringing of bells ; 

 a tumour involving the occipital region may cause a visual aura, and so 

 on. Central sensory localization is the fundamental idea of the old 

 doctrine of the specific energy of nerves, which, in modern phraseology, 

 expresses the fact that excitation of the central end of a sensory nerve 

 by various kinds of stimuli causes always or at least very often the 

 particular kind of sensation appropriate to the nerve. 1'he observation 

 so frequently made in surgery before the days of anaesthetics, that when 

 the optic nerve was cut in removing the eyeball the patient experienced 

 the sensation of a flash of light,* was long looked upon as the strongest 

 prop of the law of specfic energy, and well illustrates the meaning of the 

 term. Here a mechanical excitation of the optic fibres in their course 

 gives rise to the same sensation as excitation of the retina by the 



* It is said that this is not always the case. 



