Vital action means food and stimulus. Limit of power. can grow or act separately, and the importance of observing the relative time and quantity of action in each part. We now want to determine some of the forces or causes which may regulate the time and quantity of action in the parts of living things. I must crave your indulgence if I here assume an hypothesis which I have endeavoured to illustrate and support by evidence given elsewhere. Vital acts only must be observable in living things which must be supplied with pabulum or food material and also stimulated by some force. The forces which thus stimulate acts of nutrition, appear also to determine and control the time and the quantity of action. In the work referred to, numerous examples are classified, where nutrition of parts of living things is controlled by such forces as light, heat, sound, pressure, gravity, &c. Time, however, prevents me repeating my evidence here. We have considered thus far what to observe in looking at Nature's work in living things, and I have referred to my hypothesis as to the mode in which physical force controls vital acts. There is however, obviously, a limit to the capacity of every living thing for the performance of its functions. In seeking to observe these limits, we must first determine the outcome of its action, and how it is to be observed. In each living thing there is an intrinsic tendency to continue its growth for a certain period, and up to a certain amount; this appears to be due to inherited antecedent impressions, but the tendency may be altered in succeeding generations. Cultivation and training may increase capacity for action in an indicapacity. vidual, as well as in a species. Cultivation of the apple tree in successive generations has improved the capacity for producing large fruit; cultivation of the carrot gives us large roots in comparison to the small ones found in the wild species. Cultiva tion increases As regards the individual, the capacity for action may Feeding. be determined by feeding, or by the conditions of stimulation. A sensitive plant, if well fed, becomes very slightly sensitive to a blow, and will not move its leaflets; an animal deprived of food soon loses its motor power. The intellectual capacity of children may be increased by feeding when the previous diet has been deficient (see Report of Birmingham Committee). Over-feeding is equally undesirable, especially just before lessons. By the proper employment of exercise for every organ and part of the body, we may increase capacity for action by stimulating to the full the nutrition of each part. and stimu There is a limit to the capacity for function in every Feeding living thing, but if the food supply is sufficient, the quan- lating. tity of nutrition is directly proportional to the amount of stimulation, up to a certain amount. When growth in a child is deficient from want of food, feeding may be a most potent factor in augmenting the capacity for action. When feeding has been sufficient and stimulation or exercise defective, the course of management is obvious. There are cases of defective nutrition of the body where high feeding is very necessary, especially among some nervous children. When I say that the capacity for action may be increased or diminished by stimulation, I mean by such physical conditions as pressure, touch, light, the sight of objects, or sound (see Catalogue). Diminished stimulation of a muscle leads, not only to less work done, but also to wasting of its substance; it is not sufficient for nutrition and good work of the muscle that it be supplied with blood, it must also be stimulated and exercised. Probably there is much less limitation to the growth of a crystal than of a living thing. Limited Increasing We may try to cause variation in the limit of capacity capacity. for action, and probably it is easier to increase the quantity of action than its duration. There is a more distinct limit to the duration of life than to the quantity of action that shall occur during the period of life. The leaf of a tree has its own period for duration of life, apart from the effects of late springs and early autumns. The duration of leaves of many trees separate (Gray, p. 87) from the a leaf. stem, and fall by means of an articulation at the junction with the stem, which begins to form early in the season and is completed at the close. There is a kind of disintegration of a transverse layer of cells, which cuts off the petiole by a regular line, and leaves a clean scar. Intrinsic causes, acting in the plant, probably due to impressions made upon the ancestors by their surroundings, determine the duration of life of the leaf. In each living thing there is a tendency to grow for a certain period, and up to a certain amount. Nature guides thinking. In the infant, before birth, conditions of development occur which cannot proceed after birth, e.g. closure of certain openings and fissures. An ovule of the flower is a cellular body, it has but a small capacity for growth, and this lasts but a short time, unless it be fertilized or stimulated by the advent of a pollen grain. Fertilization stimulates the ovule and increases the capacity for nutrition and growth so that under favourable circumstances it developes into a seed. These two last are examples of altered capacity for growth. The study of Nature may guide us in all things, in observing and in thinking: in such work we must constantly make analogies and generalisations. Certain generalisations as to what to observe, and how to describe what we see, have been stated in pursuing our studies of plant life; how can we apply them to the study of children? This will be shewn presently. We have seen the importance of the separate action of the different parts of the living thing observed, and their impressionability to control by forces around. a child and In applying any generalisations from the study of Analogy of plant-life to the observation of children, we make anȧ- plant. logies. We studied the germinating seeds, the turnip, the carrot and potato, the convolvulus and the ivy, and made some generalisations as to Nature's methods of action in living things. What does the potato shew us as to what to observe in a child's body or his brain? We find that it is necessary to observe the separate parts A potato, its parts. of the potato and the parts of the child that can move and act separately. We may place the potato and the child side by side, but what we compare in them is not the actual vital process in each but the time and the quantity of action in the parts of each; we find resemblance or analogy between the potato and the child in the fact that separate parts of each can grow and display action separately. In reality we do not compare the potato and the child directly, but the attributes of the nutritive processes in each, and we find that it is convenient to describe facts seen in the child, according to the methods used in describing the simpler organization of plants. A system of methodical procedure is thus put forward as a guide to the complex problems before us in our subsequent work. The studies of the astronomers were without fixed method and system till the minds of Kepler and Newton put forward definite modes of thought and observation (see Stewart's Philosophy). Aptness is a term given to a quality possessed by Aptness. some living things, and indicates a condition of predisposition for action. A child who is ordinarily attentive and predisposed to study, may be said to be apt to learn, Aptness in or readily impressed by education. It will be well to plants. illustrate aptness in the lower members of Nature's work. In the growth of the tissues of plants, chlorophyll grains play a very important part, decomposing carbonic acid. gas under stimulation by light, thus supplying carbon to the plant. Professor Goodall (p. 287) says concerning this process:-"In regard to the genesis of the chlorophyll granules which are the essential constituents of the assimilative cells, the following view appears to be most in consonance with recent investigations. Imbedded in the protoplasm of every growing point there are peculiar bodies (plastids) which have substantially the same characters and structure as the protoplasm, and are more or less clearly differentiated from it even at an early period. As the cells, which develope from the growing point, assume the different characters which fit them for special service, for example, those in certain tubers and roots for store-houses, those in leaves for assimilation, and those in some flowers and fruits for colour, their plastids may likewise assume special characters. Those which are destined for the store-houses become leuco-plastids, or starch-formers; those in green tissue, chloro-plastids, or chlorophyll granules; and those in coloured flowers and fruits, chromo-plastids. As might be expected from their common.origin, the plastids, which under one set of conditions might become leuco-plastids, may, under another set, become chromo-plastids, etc." The aptness, in plants, for various conditions appears to be due to the 'plastids.' The chromo-plastids afford examples of structures shewing aptness for various kinds of work which vary according to the conditions which surround them. The Mimosa pudica, if well sunned during the day, drops its leaves more readily at night; sunlight makes it apt for |