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Published online by Cambridge University Press: 19 February 2018
Man is born with a nervous system of the highest type, and in accordance with what we know concerning the laws of hereditary transmission, with one which—though at the time of birth so far advanced morphologically as clearly to foreshadow its future excellence—we are entitled to believe possesses within itself certain potentialities of organic development, definite enough and powerful enough to ensure its evolution in given directions, so long as its different parts are acted upon by those stimuli to which they have been accustomed in the preceding individuals of the parent race. To a certain extent the infant is even born already possessing capabilities of receiving impressions and of executing movements—corresponding parts of its nervous system being more advanced than others in histological development. And it may be stated generally, that these capabilities and these powers are gradually strengthened and extended in a definite order, as particular parts of the nervous system advance towards a more perfect development of tissue—that is to say, as nerve-cells and communicating nerve-fibres gradually arise out of the less specialised embryonic tissue which formerly occupied their place.
∗ See Herbert Spencer's “Principles of Psychology” for a full exposition of this doctrine.Google Scholar
† In minor details I am fully aware this is believed not to be the case in the opinion of the best judges and if there is one thing more striking than another distinguishing the brain of man from that of the higher apesf it is the fact that in the former there has risen a very slight though still perceptible want of symmetry between the convolutions of the two hemispheres.Google Scholar
∗ Dr. Maudsley seems to hint at some such relation as this, though he does not specify that the perceptive act and the emotional resultant pertaining to it have their origin in the same areas of grey matter, when he says, “Emotion is strictly perhaps the sensibility of the sapremo centres to ideas.” (The Physiology and Pathology of Mind, p. 47.)Google Scholar
∗ Converting them in fact into what I call Perceptions using this term in its ordinary psychological acceptation.Google Scholar
† For some of the applications of this doctrine the reader may consult a paper “On the Physiology of Thinking,” and also one “On the various forms of Loss of Speech in Cerebral Disease,” in the current Nos. of the Fortnightly Reviem, and of the British and For. Med. Chirurg. Review.Google Scholar
∗ Whilst believing, therefore, in a doctrine of uniformity, as regards the transmission, &c., of nerve stimuli, it would seem that though this is the general rule, still where injuries or lacerations of substance have taken place that a stimulus is capable of making its way along unaccustomed routes, so long as anastomoses exist, by whioh it may pass continuously from nerve-cell to nerve-fibre. This is found to be the case in the transmission of sensory stimuli upwards through the spinal cord the transit is effected so long as the continuity of the grey matter is not entirely severed in any one region. It seems to be that the passage of an impression through nerve tissue from periphery to centre, or from centre to oentre, accommodates itself to altered conditions in the same way that a stream of water would, if, flowing down a moderately steep incline, it came to a place where its main bed was dammed up, whilst collateral channels were present by whioh it might pursue its onward course.Google Scholar
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