Here again we are not to expect a perfect correspondence at all points. As we shall see, apparent simplicity of the psychical phenomenon may go with a considerable complexity of the physiological process. As has been already hinted, every sensation probably involves the action of more than one sensory fibre. Not only so, there is good reason to suppose that, since every sensory process calls forth some motor reaction, even the simplest sensations are really complicated by the addition of the psychical equivalent of a motor or muscular action.1

§ 136. Correlation in Mode of Combination. In the second place, we have to inquire whether the mode in which psychical elements combine in what we call our mental life has its correlative in the physiological sphere. As we have not yet entered upon our analysis of consciousness so as to be able to define its precise form, we can only at this stage indicate in a rough manner the nature of this correlation.

Our mental life may be provisionally defined as a continuous succession of psychical states, of which the ultimate elements are sensations and other apparently simple phenomena. These combine in complex wholes, and one whole is succeeded by another whole without break and by a gradual process of transition, the successive continuity being commonly described by the figure of a stream. In this flux it is noticeable that certain elements are wont to stand out distinctly, whereas others remain obscure. Lastly, the higher developments of mental life imply a still more complex form of psychical activity, a reflective going back on the successive contents, the discrimination of these one from another, and the grouping of them according to their relations of similarity, etc. This reflective elaboration enters into all clear thinking, which, as we shall see, is relating and uniting, and underlies what we call the permanent consciousness of self.

The totality of the nervous processes concerned in mental life, different as it undoubtedly is from this, yet appears to supply a certain physical basis for it. As we have seen, the brain is a great meeting-place of the results of nervous stimulation. Its manifold connexions with the peripheral (including the internal vital) organs ensure a continuous supply of excitation, and change in the form of excitation. Again, the continuity of its structure seems to supply a physical

It follows that to talk as certain physiologists do of a sensation or idea having its own particular cortical cell is unwarranted.

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condition for the processes of psychical elaboration. In order to make it serve still more completely for a physical basis of conscious life, we have to assume two additional features. First of all we must postulate in the structure of the brain a special apparatus, by help of which particular psychical constituents may be intensified and raised into distinct consciousness. Such an apparatus is now supposed to be supplied by a group of motor centres which, as we shall see, specially subserve the process of attention. Secondly, we must assume as the physical basis of all that we mean by the retention and reproduction of psychical elements that the brain substance is endowed with a conservative property, by help of which the effects of peripheral stimulation are somehow stored up so as to enable the structures to afterwards re-enter upon the state of excitation independently of peripheral stimulation. Such a conservation of the traces of former action is now supposed to be a common property of living organs.

While we may thus recognise a certain correspondence between the general form of cerebral action and that of our mental life, we must not seek to force the correlation to the point of overlooking the disparateness between the two. Just as a sensation, say of tone, is something totally dissimilar to the molecular vibrations in a nerve which condition it, so the complex processes of thought differ in kind from any conceivable arrangement of physical actions. Thus, as we shall see when we come on to consider the work of intellectual elaboration, we cannot expect to find among physical movements an analogue to what we call a consciousness of difference or of likeness between two impressions, or a recollection of something as past. These psychical actions are sui generis, and cannot therefore be brought into analogy to movements of a material substance. All that we can say is then that just as the multiplicity of psychical elements (sensations, etc.) is somehow conditioned by a multiplicity of disparate nervous actions, so the organic unity and form of our mental life is somehow maintained by the presence of certain nervous arrangements.1

§ 14. Practical Bearing of the Correlation. The correlations between psychical and physical action just traced out have an obvious practical bearing. The fact that every psychical process is correlated with and conditioned by a physical one, that our mental life is made up of a group of psycho-physical processes, makes it imperative that in guiding, controlling, and economising the mental activities we should constantly

1 On the correlations of psychical and cerebral action, see Ladd, Elements of Physiol. Psychology, p. 579 and following.

refer to the physiological conditions. Since the amount of mental activity at any time depends directly on the amount of disposable cerebral energy, it becomes a matter of the first consequence in order to secure the most efficient thought and action that we should satisfy the conditions of vigorous cerebral action. Brain-power may be lowered by want of nutrition, by insufficient supply of oxygen, by any organic cause tending to enfeeble the body generally, as also by fatigue of the brain itself. The old maxim, 'A sound mind in a sound body,' becomes in modern scientific language, "A vigorous discharge of the mental functions has for its immediate physical basis a healthy and well-nourished condition of the brain".

course.

§ 15. Cerebral and Mental Development. Again, the general correlation of brain-action and mental process becomes of importance to the psychologist in tracing the course of psychical development. There is good reason to suppose that the brain and the mind develop pari passu. The growth of the brain as compared with that of the whole body follows a curious As common observation tells us, the brain at birth is greatly in advance of the body both in size and in weight. It almost reaches its maximum size by about the end of the seventh year. After this it undergoes a prolonged process of development, in which its elements (cells and fibres) multiply in number, more numerous connexions between cell and cell are built up, and the several distinctly-marked regions (folds or convolutions) become better defined. There is, moreover, a certain order in the development of the different cerebral organs, the parietal and frontal lobes appearing to develop latest. This development of the cerebral organs presumably keeps pace with and serves to determine the advance of mind. It is highly probable that all mental progress, all acquisition of new ideas and new capabilities, involves the formation of new nervous paths, connecting one region of the centres with another, and facilitating the co-operation of these in single complex processes.

As we shall see by-and-by, the whole movement of psychophysical development may be regarded as a double one. In the first place repeated or recurring processes of thought and

1 So Bischoff, Das Hirngewicht des Menschen, p. 171.

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action become more perfectly organised, and as a consequence more rapid and unconscious or automatic. This result is expressed by the term Habit, a principle which obtains in the whole of our mental life, and which will be specially studied in connexion with movement and action. This transformation of conscious into semi-conscious or automatic action depends, it is evident, on the perfect co-ordination of certain central elements. In the second place there is a continual advance to new psychophysical acquisitions. Thus so long as development goes on we move on to new combinations of ideas, more complicated processes of thought, and so forth. This involves on the physiological side the prolonged plasticity of the cerebral substance, the capability of developing new nervous elements, and new organic attachments between these. The development of the nervous mechanism is thus seen at once to diminish the sphere of distinct consciousness in certain directions (the familiar and habitual) and to a much larger extent to extend this sphere in other directions (the new and more complex forms of psychical activity).

§ 16. Physical Substrate of Individuality: Temperament. While the nervous system thus subserves the common typical form of the mental life, it constitutes also the basis of individual character. It is a fact familiar to all good observers of children that clearly-marked differences in mental aptitude and disposition show themselves within the first years of life. These facts, which point to an original and connate idiosyncrasy or individual character, appear to necessitate the supposition that the nervous system, though exhibiting the same typical plan in all human beings, differs to some extent in its proportions in the case of different individuals. Observation has shown that exceptional powers of intellect are correlated with special richness of convolution; and it is probable that such extraordinary complexity of structure is predetermined by the congenital conformation of the brain. Not only so, there is little doubt that differences of mental disposition, as that between the quick, lively and the slow, tenacious mind, have their physiological counterpart in functional differences of the nervous system. The old doctrine of Temperament was a crude attempt to fix the physical substratum of such individual differences. A more complete knowledge of the nervous system and its mode of

action may one day enable the physiologist to substitute a truly scientific doctrine of temperament.

Modern science has familiarised us with the idea of a hereditary transmission of mental as well as of physical character. The nature of such hereditary transmission will be considered later on. Here it is enough to point out that the transmission of any special aptitude, taste, or moral inclination from parent to child takes place through the medium of the nervous system. To every distinct inherited trait or tendency of mind there corresponds presumably some peculiarity in the original constitution or set of the individual's nervous system. In this way we all bring into the world, wrought into the very texture of our brain-centres, the physical basis of our future individual character, mental and moral.

The doctrine of temperaments, which we owe to Galen, classified the observable differences of disposition under four heads, thus: (1) the sanguine or "full-blooded" temperament, which is warm, impressionable, and changeable; (2) the phlegmatic or "full-phlegmed," which is quiet, slow, and persistent; (3) the choleric or full-biled," which is energetic, with predominant objective attitude; and (4) melancholic or “black-biled," which is sentimental, with a marked tendency to subjectivity. It is needless to say that this classification, so far as the physical bases are concerned, is scientifically valueless. At the same time, it served to mark off some well-recognised differences of disposition; and recent writers on the subject have made Galen's classification their starting-point, and endeavoured to account for the manifold differences of disposition by variously combining the four features here distinguished.1

REFERENCES FOR READING.

For a fuller account of the Nervous System in its connexions with mind the reader is referred to the elaborate treatise of Ladd, The Elements of Physiological Psychology. Among the best recent accounts (in English) of the Brain and its functions are Ferrier's Functions of the Brain; M. Foster's Text-Book of Physiology, part iii. chap. ii.; and the résumé given y W. James, The Principles of Psychology, vol. i. chap. ii. Other authors with consulting are Bastian, The Brain as Organ of Mind; G. H. Lewes, Physical Basis of Mind; and Maudsley, The Physiology of Mind. Interesting illustrations of the interaction of Body and Mind are given by Lotze, Microcosmus (English transl.), book iii. chap. iii.

1 For an account of Galen's doctrine of temperaments, see Siebeck, Geschichte der Psychologie, ii. 278. On the problem of classifying temperaments, see Lotze, Microcosmus (English transl.), book vi. chap. ii.; Ladd, Elements of Physiol. Psychology, p. 574 and following. An ingenious attempt to build up a classification of temperaments on Galen's basis will be found in a recent work, Our Temperaments, by A. Stewart,