A Lecture on the Preservation of Health | Page 2

attention, and an accurate acquaintance with the extensive science of medicine, to combat it; to attain this knowledge demands the labour of years. But, a majority of the diseases to which we are subject, are the effects of our own ignorance or imprudence, and it is often very easy to prevent them; mere precepts however, have seldom much effect, unless the reasoning upon them be rendered evident; on this account, I shall first endeavour, in as plain and easy a manner as possible, to explain to you the laws by which life is governed; and when we see in what health consists, we shall be better enabled to take such methods as may preserve it. Health is the easy and pleasant exercise of all the functions of the body and mind; and disease consists in the uneasy and disproportioned exercise of all, or some of the functions.
When dead matter acts upon dead matter, the only effects we perceive are mechanical, or chemical; for though there may appear to be other kinds of attraction, or repulsion, such as electric and magnetic, yet these come under the head of mechanical attraction, as producing motion; we may therefore lay it down as a law, that when dead, or inanimate bodies act upon each other, no other than mechanical, or chemical effects are produced; that is, either motion, or the decomposition, and new combination of their parts. If one ball strike another, it communicates to it a certain quantity of motion, this is called mechanical action; and if a quantity of salt, or sugar, be put into water, the particles of the salt or sugar will separate from each other, and join themselves to the particles of the water; the salt and water in these instances, are said to act on each other chemically; and in all cases whatever, in which inanimate, or dead bodies act on each other, the effects produced are, motion, or chemical attraction.
But, when dead matter acts on those bodies which we call living, the effects are much different; let us take for example a very simple instance.--Snakes, at least some species of them, pass the winter in a torpid state, which has all the appearance of death; now heat, if applied to dead matter, will only produce motion, or chemical combination; but if it be applied to the snake, let us see what will be the consequence; the reptile first begins to move, and opens its eyes and mouth; when the heat has been applied for some time, it crawls about in search of food, and performs all the functions of life. Here then, dead matter, when applied to a living body, produces living functions; for if the heat had not been applied, the snake would have continued senseless, and apparently lifeless. In more perfect animals, the effects produced by the action of dead matter on them, are more numerous, and are different in different living systems, but are in general the following--sense and motion in almost all animals, and in many the power of thinking, and other affections of the mind. The powers, or dead matters, which are applied, and which produce these functions, are chiefly, heat, food, and air. The proof that these powers do produce the living functions, is in my opinion a very convincing one, namely, that when their actions are suspended, the living functions cease; take away, for instance, heat, air, and food from animals, and they soon become dead matter, and it is not necessary that an animal should be deprived of all these to put a stop to the living functions; if any one of them be taken away, the body sooner or later becomes dead matter: it is found by experience, that if a man be deprived of air, he dies in about three or four minutes; for instance, if he be immersed under water; if he be deprived of heat, or in other words, exposed to a very severe degree of cold, he likewise soon dies; or if he be deprived of food, his death is equally certain, though more slow. It is sufficiently evident then, that the living functions are owing to the action of these external powers upon the body. What I have here said, is not confined to animals, but the living functions of vegetables are likewise caused by the action of dead matter upon them. The dead matters, which by their action produce these functions, are principally heat, moisture, light, and air. It clearly follows therefore, from what I have said, that living bodies must have some property different from dead matter, which renders them capable of being acted upon by these external powers, so as to produce the living functions; for if they had not, the only effects which these powers could produce, would be