The doctrine of animal life which has been taught, exhibits in the first place, a new view of the nervous system, by discovering its origin in the extremities of the nerves, on which impressions are made, and its termination in the brain. This idea is extended in an ingenious manner by Mr. Valli, in his treatise upon animal electricity.
2. It discovers to us the true means of promoting health and longevity, by proportioning the number and force of stimuli to the age, climate, situation, habits, and temperament of the human body.
3. It leads us to a knowledge of the causes of all diseases. These consist in excessive or preternatural excitement in the whole, or a part of the human body, accompanied generally with irregular motions, and induced by natural or artificial stimuli. The latter have been called, very properly, by Mr. Hunter, irritants. The occasional absence of motion in acute diseases is the effect only of the excess of impetus in their remote causes.
4. It discovers to us that the cure of all diseases depends simply upon the abstraction of stimuli from the whole, or from a part of the body, when the motions excited by them are in excess; and in the increase of their number and force, when motions are of a moderate nature. For the former purpose, we employ a class of medicines known by the name of sedatives. For the latter, we make use of stimulants. Under these two extensive heads, are included all the numerous articles of the materia medica.
5. It enables us to reject the doctrine of innate ideas, and to ascribe all our knowledge of sensible objects to impressions acting upon an innate capacity to receive ideas. Were it possible for a child to grow up to manhood without the use of any of its senses, it would not possess a single idea of a material object; and as all human knowledge is compounded of simple ideas, this person would be as destitute of knowledge of every kind, as the grossest portion of vegetable or fossil matter.
6. The account which has been given of animal life, furnishes a striking illustration of the origin of human actions, by the impression of motives upon the will. As well might we admit an inherent principle of life in animal matter, as a self-determining power in this faculty of the mind. Motives are necessary, not only to constitute its freedom, but its essence; for, without them, there could be no more a will, than there could be vision without light, or hearing without sound. It is true, they are often so obscure as not to be perceived, and they sometimes become insensible from habit; but the same things have been remarked in the operation of stimuli, and yet we do not upon this account deny their agency in producing animal life. In thus deciding in favour of the necessity of motives, to produce actions, I cannot help bearing a testimony against the gloomy misapplication of this doctrine by some modern writers. When properly understood, it is calculated to produce the most comfortable views of the divine government, and the most beneficial effects upon morals and human happiness.
7. There are errors of an impious nature, which sometimes obtain a currency, from being disguised by innocent names. The doctrine of animal life that has been delivered is directly opposed to an error of this kind, which has had the most baneful influence upon morals and religion. To suppose a principle to reside necessarily and constantly in the human body, which acted independently of external circumstances, is to ascribe to it an attribute, which I shall not connect, even in language, with the creature man. Self-existence belongs only to God.
The best criterion of the truth of a philosophical opinion, is its tendency to produce exalted ideas of the Divine Being, and humble views of ourselves. The doctrine of animal life which has been delivered is calculated to produce these effects in an eminent degree, for
8. It does homage to the Supreme Being, as the governor of the universe, and establishes the certainty of his universal and particular providence. Admit a principle of life in the human body, and we open a door for the restoration of the old Epicurean or atheistical philosophy, which supposed the world to be governed by a principle called nature, and which was believed to be inherent in every kind of matter. The doctrine I have taught, cuts the sinews of this error; for by rendering the continuance of animal life, no less than its commencement, the effect of the constant operation of divine power and goodness, it leads us to believe that the whole creation is supported in the same manner.
9. The view that has been given of the dependent state of man for the blessing of life, leads us to contemplate, with very opposite and inexpressible feelings, the sublime idea which is given of the Deity in the scriptures, as possessing life “within himself.” This divine prerogative has never been imparted but to one being, and that is the Son of God. This appears from the following declaration. “For as the Father hath life in himself, so hath he given to the Son to have life within himself.”[103] To this plenitude of independent life, we are to ascribe his being called the “life of the world,” “the prince of life,” and “life” itself, in the New Testament. These divine epithets which are very properly founded upon the manner of our Saviour's existence, exalt him infinitely above simple humanity, and establish his divine nature upon the basis of reason, as well as revelation.