1. Sensations of the special senses, including: sight, sound, touch (including temperature), taste, and smell.
2. Motor, or muscular, sensations.
3. Organic sensations.
Sensations of the Special Senses.—As a study of the five special senses has been made by the student-teacher under the heading of physiology, no attempt will be made to explain the structure of these organs. It must be noted, however, that not all senses are equally capable of distinguishing differences in quality. For example, it seems quite beyond our power to recall the tastes and odours of the various dishes of which we may have partaken at a banquet, while on the other hand we may recall distinctly the visual appearance of the room and the table. It is worthy of note, also, that in the case of smell, animals are usually much more discriminative than man. Certain of our senses are, therefore, much more intellectual than others. By this is meant that for purposes of distinguishing the objects themselves, and for providing the mind with available images as materials for further thought, our senses are by no means equally effective. Under this heading the special senses are classified as follows:
Higher Intellectual Senses: sight, hearing, touch.
Lower Intellectual Senses: taste and smell.
Muscular Sensations.—Under motor, or muscular, sensations are included the feelings which accompany consciousness of muscular exertion, or movement. In distinction from the other sense organs, the muscles are stimulated by having nervous energy pass outward over the motor nerves to the muscles. As the muscles are thus stimulated to movement, sensory nerves in turn convey inward from the muscles sensory impressions resulting from these movements. The important sensations connected with muscular action are those of strain, force, and resistance, as in lifting or pushing. By means of these motor sensations, joined with the sense of touch, the individual is able to distinguish especially weight, position, and change of position. In connection with the muscular sense, may be recalled that portion of the Montessori apparatus known as the weight tablets. These wooden tablets, it will be noted, are designed to educate the muscular sense to distinguish slight differences in weight. The muscular sense is chiefly important, however, in that delicate distinctions of pressure, movement, and resistance must be made in many forms of manual expression. The interrelation between sensory impression and motor impulse within the nervous system, as illustrated in the figures on page [200], is already understood by the reader. For an adequate conscious control of movements, especially when one is engaged in delicate handwork, as painting, modelling, wood-work, etc., there must be an ability to perceive slight differences in strain, pressure, and movement. Moreover, the most effective means for developing the muscular sense is through the expressive exercises referred to above.
Organic Sensations.—The organic sensations are those states of consciousness that arise in connection with the processes going on within the organism, as circulation of the blood, digestion; breathing, or respiration; hunger; thirst; etc. The significance of these sensations lies in the fact that they reveal to consciousness any disturbances in connection with the vital processes, and thus enable the individual to provide for the preservation of the organism.
EDUCATION OF THE SENSES
Importance.—When it is considered that our general knowledge must be based on a knowledge of individuals, it becomes apparent that children should, through sense observation, learn as fully as possible the various qualities of the concrete world. Only on this basis can they build their more general and abstract forms of knowledge. For this reason the child in his study of objects should, so far as safety permits, bring all of his senses to bear upon them and distinguish as clearly as possible all their properties. By this means only can he really know the attributes of the objects constituting his environment. Moreover, without such a full knowledge of the various properties and qualities of concrete objects, he is not in a position to turn them fully to his own service. It is by distinguishing the feeling of the flour, that the cook discovers whether it is suited for bread-making or pastry. It is by noting the texture of the wood, that the artisan can decide its suitability for the work in hand. In fine, it was only by noting the properties of various natural objects that man discovered their social uses.