7. Death is produced by a preternatural rigidity, and in some instances by an ossification of the solid parts of the body in old age, in consequence of which they are incapable of receiving and emitting the motions of life. No more occurs here, than would happen if a stick or pipe-stem were placed in the room of catgut, upon the bridges of the violin. But death may take place in old age without a change in the texture of animal matter, from the stimuli of life losing their effect by repetition, just as opium, from the same cause, ceases to produce its usual effects upon the body. Should it be asked, what is that peculiar organization of matter, which enables it to emit life, when acted upon by stimuli, I answer, I do not know. The great Creator has kindly established a witness of his unsearchable wisdom in every part of his works, in order to prevent our forgetting him, in the successful exercises of our reason. Mohammed once said, "that he should believe himself to be a God, if he could bring down rain from the clouds, or give life to an animal." It belongs exclusively to the true God to endow matter with those singular properties, which enable it, under certain circumstances, to exhibit the appearances of life. I cannot conclude this subject, without taking notice of its extensive application to medicine, metaphysics, theology, and morals. 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.