of the action of each part, and of the series of actions in the whole subject. surround If you accept the views given as to the forces aiding Character and controlling the attributes and characters of the acts formed by of growth and action, it may appear to you probable ing influthat the child trained under certain surrounding in- ences. fluences will be impressed by them, and formed by them, and will subsequently grow in harmony with them; the surroundings largely make the character of the child. It seems to be true that when certain forces have long acted upon a living thing, and have altered its modes of growth or modes of action, that the said living thing remains impressionable to that same force or set of forces. This is in part what is meant when it is said that faculty is increased by use or exercise. In applying such principles it must be remembered that there are internal forces affecting the child's growth and action, but these intrinsic forces, which result from antecedent impressions, may be modified by the environment. In the next Lecture we shall give particular attention to the study of brain-centres and look at modes of action in them, similar to those seen in lower living things. The brain is one of the most complex organs in the body, we know that it consists of parts which can be stimulated to separate action. We want to study how the brain acts, and in such inquiry our preliminary survey of Nature will help us. CHAPTER II. STUDY OF THE BRAIN AS A PART OF THE BODY. and con observa tion. We now have to study the brain as a part of the body, and determine, as best we may, its modes of action. In the first lecture we observed certain vegetable specimens, which were.selected for their simplicity, and we found that it was often possible and convenient Widening to divide the subject observed into parts, which can act independently of one another as to time of action, or tracting the field of unequally as to quantity of action. In so doing we contracted, or limited the field of observation and thought; thus we considered action in individual groups of cells in the radicle of the pea. At other times we found reason to enlarge our field of observation, action in one subject could not be understood by looking at it alone; we understood the flower of the iris better when observing two flowers and a bee. So in now proceeding to study the brain, we begin by dividing it into parts called nerve-centres, which it has been shewn can act separately or in different ratios under varying circum Two flowers and a bee. Nerve centres and the brain. stances. Having studied nerve-centres as to their properties, we shall again enlarge our field of observation, including the whole brain, the organs of special sense, and the muscular system which is the mechanism for the expression of thought and action. cells. The brain is a soft and delicate structure, seated in the brain case and carefully protected; it consists essentially of two kinds of material, the nerve-cells, and the nerve-fibres. The nerve-cells, when duly nourished, are Nervethe makers of nerve-force; for their proper nutrition they need a good supply of blood in their vessels. A nerve- Nervefibre passes off from each cell and conveys the force fibres. generated in it, which is then called a nerve-current; Nervethere are millions of such cells in the structure of the current. brain. When the nerve-force generated by a nerve-cell is carried by a fibre to a muscle, say in the face, or in the limbs, this nerve-current causes the muscle to contract or shorten, and visible movement results, the movement being stimulated by the force sent from the nervecell. The movement seen indicates to us the time and Nervemuscular quantity of the discharge of force from the nerve-cell; movement. such movement is conveniently called a nerve-muscular movement. The substance of the brain is thus mainly made up The brain. of groups of nerve-cells, many of which are connected with one another by nerve-fibres, and many of them are connected with the muscles of the body and send nervecurrents to them, thus causing the movements of the members. The nerve-cell generates force as the outcome of its nutrition. While the brain is giving out force, it must be replenished by nutrition, or it will run down, and be less capable of producing energy after a short time, it will then need food and rest. We have spoken of the nerve-cells of the brain as Afferent nerve being connected with one another, and with the muscles fibres. Efferent nerve. fibres. Visible movement. cells of the brain, and convey currents of force from these parts respectively to the cells of the brain; such nerve-fibres are called afferent because they convey currents to the nerve-system; in distinction from these the fibres which convey currents from the nerve-cells to the muscles are called efferent. The fibres which pass in both directions are collected into bundles, or strings, and are commonly called the nerves of the body; the ingoing or afferent nerves convey stimuli to the brain, the outcoming or efferent nerves carry motor currents from the nervecells to the muscles. I desire in this lecture to indicate certain characters of the brain as data for the theory of mental action (Psychosis), and explanation of methods of observation of facts, and methods of training the mind, which will be advanced further on. The principal method by which we observe action in nerve-centres is by noting their action on muscles; a current passing from a nerve-centre to a muscle is followed by contraction of the muscle, and visible movement in the body; the muscle is the visible index of a nerve-current proceeding from the centre, indicating the time and to some extent the quantity of its action. One set of muscular contractions indicates action in one set of nerve-centres corresponding'. Further, the sequence of the muscular action is also the sequence of the action in the centres corresponding, and the antecedent of the action in the centres is the necessary antecedent of the result of the movement. This combined 1 The clinical investigations of Dr Hughlings Jackson, and the physiological inquiries of Dr Charles Beevor and Mr Victor Horseley, have shewn that while a certain movement is principally due to action in one particular nerve-centre, it may be produced in part by action in other centres. action of a nerve-centre and muscle is conveniently termed a nerve-muscular act, and such acts are often stimulated through the organs of special sense. Let me ask your attention to this diagram, it is not a Explanarepresentation of anatomical structure, but may serve our tion of diagram. Fig. 1. The brain is represented by the shading as divided into areas A, B, C, D, E which can act more or less separately: each area or section of brain is represented as connected by nerve-fibres, with a muscle corresponding. Each section of brain may receive a stimulus from the eye or the ear. The representation is purely diagrammatical for the sake of clearness of description. |