CEREBRAL PHYSIOLOGY.
By means of the nervous system, an intimate relation is maintained between mind and body, for nervous energy superintends the functions of both. The fibres of nervous matter are universally present in the organization, uniting the physical and spiritual elements of man's being. Even the minutest nerve-rootlets convey impressions to the dome of thought and influence the intellectual faculties. We recognize muscular force, the strength of the body, molecular force, molecules in motion, as heat, light, chemical force, electricity, and nervous force, a certain influence which reacts between the animal functions and the cerebrum, thus connecting the conditions of the body with those of the mind. We cannot speak of the effects of mind or body separately, but we must consider their action and reaction upon each other, for they are always associated. There are many difficulties in understanding this relationship, some of which may be obviated by a study of the development of nervous matter, and its functions in the lower orders of organization.
Within the plant-cells is found a vital, vegetable substance termed bioplasm, or protoplasm; which furnishes the same nutritive power as the tissues of the polyp and jelly fish. Many families of animals have pulpy bodies, and slight instinctive motion and sensibility, and in proportion as the nervous system is developed, both of these powers are unfolded. Plants have a low degree of sensibility, limited motion, respiratory and circulatory organs. Animals possess quicker perceptions and sensibilities, the power of voluntary motion, and, likewise a rudimental nervous system. Some articulates have no bony skeleton, their muscles being attached to the skin which constitutes a soft contracting envelope. One of the simplest forms of animal life in which a nervous system is found, is the five-rayed star-fish. In each ray there are filaments which connect with similar nerve-filaments from other rays, and form a circle around the digestive cavity. It probably has no conscious perception, and its movements do not necessarily indicate sensation or volition. In some worms a rudimentary nervous system is sparingly distributed to the cavities of the thorax and abdomen, and, as in the star-fish, the largest nerve-filament is found around the esophagus, presiding over nutrition.
A higher grade of organization requires a more complete arrangement of nervous substance. Stimulus applied to one organ is readily communicated to, and excites activity in another.
The nervous system of some insects consists of two long, white cords, which run longitudinally through the abdomen, and are dilated at intervals into knots, consisting of collections of nerve-cells, called ganglia. They are really nerve-centers, which receive and transmit impulses, originate and impart nervous influence according to the nature of their organic surroundings. The ganglia situated over the esophagus of insects correspond to the medulla oblongata in man, in which originate the spinal accessory, glosso-pharyngeal, and pneumogastric nerves. The latter possess double endowments, and not only participate in the operations of deglutition, digestion, circulation, and respiration, but are also nerves of sensation and instinctive motion. The suspension of respiration produces suffocation. In insects, these ganglia are scarcely any larger than those distributed within the abdomen, with which they connect by means of minute, nervous filaments. Insects are nimble in their movements, and manifest instinct, corresponding to the perfection of their muscular and nervous systems. When we ascend to vertebrates, those animals having a backbone, the amount of the nervous substance is greater, the organic functions are more complex, and the actions begin to display intelligence.
Man possesses not only a complete sympathetic system, the rudiments of which are found in worms and insects, and a complete spinal system, less perfectly displayed in fishes, birds, and quadrupeds, but, superadded to all these is a magnificent cerebrum, and, as we have seen, all parts of the body are connected by the nervous system. The subtle play of sensory and motor impulses, of sentient and spiritual forces, indicates a perfection of nervous endowments nowhere paralleled, and barely approached by inferior animals. This meager reference to brainless animals, whoso knots of ganglia throughout their bodies act automatically as little brains, shows that instinct arises simultaneously with the development of the functions over which it presides. Here begins rudimentary, unreasoning intelligence. It originates within the body as an inward, vital impulse, is manifested in an undeviating manner, and therefore displays no intention or discretion. While Dr. Carpenter likens the human organism "to a keyed instrument, from which any music it is capable of producing can be called forth at the will of the performer," he compares "a bee or any other insect to a barrel organ, which plays with the greatest exactness a certain number of tunes that are set upon it, but can do nothing else." Instinct cannot learn from experience, or improve by practice; but it seems to be the prophetic germ of a higher intelligence. It is nearly as difficult to draw the dividing line between instinct and a low grade of intelligence, as it is to distinguish between the psychical and psychological[4] functions of the brain.
The intimate relation of instinct to intelligence is admirably illustrated in the working honey-bee. With forethought it selects a habitation, constructs comb, collects honey, provides a cell for the ova, covers the chrysalis, for which it deposits special nourishment, and is disposed to defend its possessions. It is a social insect, lives in colonies, chastises trespassers, fights its enemies, and defends its home. It manifests a degree of intelligence, but its sagacity is instinctive. Reason, though not so acute as instinct, becomes, by education, discerning and keenly penetrative, and reveals the very secrets of profound thought. We recall the aptness of Prof. Agassiz's remark: "There is even a certain antagonism between instinct and intelligence, so that instinct loses its force and peculiar characteristics, whenever intelligence becomes developed." Animals having larger reasoning powers manifest less instinct, and some, as the leopard, exercise both in a limited degree. This double endowment with instinct and low reasoning intelligence, is indicated by his lying in ambush awaiting his prey, the hiding-place being selected near the haunt of other animals, where nature offers some allurement to gratify the appetite.
Simple reflex action is an instinctive expression, manifesting an intuitive perception, almost intelligent, as shown by the contraction of the stomach upon the food, simply because it impinges upon the inner coats, and thus excites them to action. A better illustration, because it displays sympathy, is when the skin, disabled by cold, cannot act, and its duties are largely performed by the kidneys. Though reflex action is easily traced in the lower organic processes, some writers have placed it on a level with rational deliberation. Undoubtedly, all animals having perception have also what perception implies—consciousness—and this indicates the possession, in some degree, of reason. Compound reflex action extends into the domain of thought. Simple reflex action, or instinct, answers to the animal faculties, such as acquisitiveness, secretiveness, selfishness, reproductiveness, etc., and accomplishes two important purposes; self-preservation and the reproduction of the specie. With many persons, these appear to be the chief ends of life!
The psychical functions connect, not only with animal propensities, but also with the highest psychological faculties. Instinct is the representative of animal conditions, just as the highest spiritual faculties are indicative of qualities and principles. The consistent mean of conduct is an equilibrium between these ultimate tendencies of our being. The psychological functions render the animal nature subservient to the rule of purity and holiness, and deeply influence it by the essential elements of spiritual existence. The psychical organs sustain an intermediate relation, receiving the impressions of the bodily propensities, and, likewise, of the highest emotions. Obviously, these extreme influences, the one growing out of animal conditions, the other, the result of spiritual relations, pass into the psychical medium and are refracted by it, or made equivalent to one force. The body requires the qualifying influences of mind. The tendencies of the animal faculties are selfish and limiting, those of the emotive, general, universal. The propensities, like gravity, expend their force upon matter; the emotions pour forth torrents of feeling, and produce rhapsodies of sentiment. The propensities naturally restrict their expression to a specific object of sense; the emotions respond to immaterial being. The tendencies of the former are acquisitive, selfish, gratifying; of the latter, bestowing, expanding, diffusing. The one class is restricted to the orbits of time and matter, the other flows on through the limitless cycles of infinity and immortality. The former is satiated in animal gratification, the latter in spiritual beatification. The one culminates in animal enjoyment, the other expands to its ultimate conceptions in the perfections of Divine Love.
In the present life, mind and body are intimately connected by nervous matter. In this dual constitution, the spiritual mental, and animal functions are made inseparable, and modify one another. The ultimate tendencies of each extreme exist, not absolutely for themselves, but for qualifying purposes, to establish a basis for the deeper economy of life. By the employment of reason, animal and spiritual experiences are mutually benefited, and the consciousness rendered accountable. The bodily and mental workings are in many senses one, and help to interpret each other.
Every fact of mind has many aspects. A brain force, which results in thought, is simultaneously a physiological force, if it influences the bodily functions. Likewise, spiritual conceptions take their rise in the same blood that feeds the grosser tissues. This vital fluid is momentarily imparting and receiving elements from all the bodily organs, and these, in turn, must influence the process of thought, and, in a degree, determine its quality. The delicate outline, yea, even the substance of an idea, may depend upon the condition of the animal organs. Thought is subject to the laws of biology, and, therefore, is a symbol of health. Morbid conditions of the system hang out their signs in words and utterances. Words which express fear are as true symptoms of functional difficulty as is excessive palpitation. The organ representing fear sustains a special relation to the functions of the heart both in health and disease. Bright hopes characterize pulmonary complaints as certainly as cough. Exquisite susceptibility of mind indicates equally extreme sensibility of body, and those persons capable of fully expressing the highest emotions are especially susceptible to bodily sensations. Tears are physical emblems of grief, and fellow-feeling calls forth sympathetic tears. Excessive anxiety of mind produces general excitability of body, which soon results in chronic disease. Pleasurable emotions stimulate the processes of nutrition, and are restorative. This concomitance of mental and bodily states is very remarkable. Joy and Love, as well as jealousy and anger, flash in the eye and mould the features to their expression. Grief excites the lachrymal, and rage the salivary glands. Shame reddens the ears, drops the eyelids, and flushes the face; but profligacy destroys these expressions. The blush which suffuses the forehead of the bashful maiden betrays her love, and maternal love, stirred by the appeals of an idolized infant, excites the mammary gland to the secretion of milk. The sigh of melancholia indicates hepatic torpor, thus showing a special relation between the liver and respiratory organs. These conditions of mind and body react upon one another. Even the thought of a luscious peach may cause the mouth to water. The thought of tasting a lemon fills the mouth with secretions, and a story with unsavory associations may completely turn the stomach.
The relationship of mental and physical functions may be illustrated by entirely removing the spleen of an animal, as that of a dog. An invariable result of its extirpation is an unusual increase of the appetite, for at times the animal will eat voraciously any kind of food. The dog will devour, with avidity, the warm entrails of recently killed animals, and thrive in consequence of such an appetite. Another symptom, which usually follows the removal of the spleen, is an unnatural ferocity of disposition. Without any apparent provocation, the animal will attack others of its own, or of a different species. In some instances, these outbursts of irritability and violence are only occasional, but the experiments show quite conclusively that the spleen moderates combativeness, restrains the appetite, and co-operates with the will and judgment in controlling them.
We shall briefly consider the practical question whether the elements of mind can be ideally arranged and presented, so as to more completely reveal their relations to, and disclose their effects upon the bodily functions. Modern philosophers conceive that mind consists of a triad of essentials; Intellect, Emotion, and Volition. Physiologists assign to the cerebrum its functions, and neurological, as well as phrenological writers, have located them as represented in Fig. 68. True, there is no structural division between the parts of the cerebrum to indicate this diversity of function, nor is there any perceptible limit between the sensory and motor filaments of the game nerve. As no one has any reason for denying that separate portions of the brain may manifest distinct functions of the mind, we shall assume it as a conceded proposition. The regions of the cerebrum, thus ideally represented, occupy but little more than half of the arc of a circle, whereas it is evident that the base of the nervous mass is not idle, and is equally entitled to our consideration. In the posterior chamber of the skull is the cerebellum, anterior to, and below which, is the medulla oblongata, connecting with the spinal cord and sympathetic system. These various parts are essential to the harmonious blending of mind and body. To this end, two conditions are necessary. (1.) All the nervous forces must be so related that action and reaction may be fully established. (2.) A complete nervous circuit is requisite for the reciprocal influence of mind and body.
Nature answers to mind in physical correspondences. The planetary system is fashioned after a circle. Life itself springs from a spherule of forces. The perfection of an idea, or the completeness of a conception may be expressed by a circle. The elements of Science, Astronomy, Geology, and Natural History, are pictorially represented in this manner. How appropriately and logically can a fragment of natural history, this epitome of all nature and science—the mind—be illustrated by a simple circle! Every element must act and react, and be equal and opposite. Thus may the existence of the opposing energies and functions of each faculty be equally represented. The contrast aids us in understanding their ultimate tendencies, and enables us to correctly value and define their nature. Faculties of kindred qualities may be grouped together, and their antagonisms represented in the opposite arc of the circle. Let us employ a circle to represent mind. The conception of the abstract quality of good, requires contrast with one of a converse nature, bad, (see Fig. 69). Opposite faculties may be portrayed in the same manner. The functions of the cerebrum and spinal system may be symbolically represented as those of the highest and lowest organs, thus giving rise to the positive and negative extremes of feeling. The writer conceives of no other way in which the widely contrasted facts of human experience can be so perfectly symbolized. Good (Fig. 69) may represent moral faculties, and bad, their opposites. Undoubtedly, nature is not so arbitrary in her arrangements as we are in shadowing forth our imperfect conceptions, yet is not this a decided improvement in determining cerebral faculties and their relations? We observe how scholars and philosophers confound the noblest and most exalted emotions with the animal propensities instead of distinguishing between them. "The emotions are a department of the feelings, formed by the intervention of intellectual processes. Several of them are so characteristic that they can be known only by individual experiences; as Wonder, Fear, Love, Anger." See Logic: Deductive and Inductive, by Alexander Bain, LL. D., page 508, (1874).
This is not an exceptional, but a common example of classifying Love, the highest and purest of the emotions, with Anger, an animal propensity. Is it not more practical and philosophical to group the emotional faculties together, and upon an opposite arc represent their antagonistic energies, the ultimate tendencies of which are criminal? Both groups are mutually modifying and restraining; the one relates instinctively to the bodily wants, the other to the requirements of mind, and each is essential to a consistent life. Accordingly, we deem it philosophical to consider words as symbols of mental faculties, and to classify together such spiritual unities as joy, hope, faith, and love, the tendencies of which are to quicken and transform the ultimates of carnal life into the rudiments of an immortal one, the beginning of heaven on earth. These restrain those opposites, which lead to crime and death. Love and Hate are as antagonistic as heat and cold, and the usefulness of both depends upon their proper temperament. Fig. 70 represents the antagonism of the Intellectual faculties to the Animal, the Emotional to the Criminal, the Volitive to the Enfeebling. It is not essential to discover in the nerve-substance the precise power from which an impulse originates. We may reasonably interpret the functions of the brain, and yet be unable to disclose the duties of any ganglionic corpuscle composing it. We may foretell what each season of the year will bring forth, when we cannot forecast the history of a blade of grass or a single grain of any kind. We may predict the amount of rain for a month, and be unable to prognosticate correctly, the character of any storm, or give the history of a special drop of water. Although we cannot follow the movements of individuals in a battle, yet we may predict the result of the combat; and thus, we judge of the functions of the brain without the ability to reveal the actions of one of the organic molecules of which it is composed. We aim to give a general, reasonable, and popular description of cerebral functions and their bearing upon health and disease.
