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small end, and roll towards the great; the consequence is, that the bandage will not stay up, but constantly falls down towards the small end ; because the last round of the roller forming a greater circle than the former, slips over it, and so alternately, till the whole falls down: whereas, were they to begin at the great end, the last round of the roller forming a lesser circle than the former, would support it, and so support each other to the end. This is an instance of prejudice, shutting impenetrably the understanding, against the irresistible rays of mathematical demonstration, which the sceptic who doubts his own existence, never doubted.
Nor can such an instance be found a
mong the vulgar and illiterate; but when we look at their theories, we cannot be surprised at any practice. I shall take notice of only one, the doctrine of inflammation; and I would not have done that, had it not been perfectly analogous to the subject I am about to treat of *, and to show
* Inflammation in the animal body may be defined, an
unequal distribution of the blood.
Canker in fruit trees may be defined, an unequal distribution of the sap; but to follow out the analogy would carry us too far from the subject immediately in view. This, however, may perhaps be the subject of future discussion: but every body knows, that there are two ways of making a vessel carry easy, by lessening the contents, and by enlarging the capacity of the vessel.
The first (blood letting) is used as the only one ap
plicable with success, on the animal body ; the other (removing the outer bark) on: fruit trees; and both
the power of education, which will make men believe any thing. It will, no doubt, be thought presumption, to call in question a doctrine which has the law of prescriptive right in its favour; and it will be reckoned something worse, to differ in opinion and practice, from what has prevailed since the creation of the world: but we are of opinion that no time can make right that which is wrong, nor wrong that which is right. Inflammation, we are taught, is owing to an increased impetus of the blood, in the vessels of the part inflamed, occasioned by an increased action of the vessels of that part itself, and at the same time, there is an accumulation of the blood in these very vessels in that part. This would appear mysterious to any person who had not studied physic, how there can be an accummulation of blood, where the propelling power is increased : but to medical people it is quite intelligible. We do not know what an engineer would think, but a physician is not obliged to think like an engineer.
these operate in the same way: by relaxing the whole fluid system, and so enabling every part to maintain and perform its proper functions, and giving any weakened or injured part, an opportunity of recovering its lost power. For it is easily understood, that while every part performs its functions in due proportion to the whole, no disease will ensue ; but if, in any way; the balance is lost, inflammation will take place in the
one, and canker in the other.
We have indeed heard of a wonderful stone
in some place of Scotland, which moves by a gentle touch, but if a greater force is applied, it will not budge.
Historians relate this story, but they do not, so far as I know, attempt to account for it; but they wrote before the invention
We explain inflammation by spasm, which stops the blood in its course, and an increased action of the vessels which pushes it on, and both these are produced by the vis medicatrix naturae. This kind of reasoning is not confined to physic alone; for when men cannot explain any of the phenomena of nature, in one progressive series of cause and effect, they set up two opposite agents, the one to do good, the other to do ill; and the magic lanthorn is carried over the world,-Pull baker, pull devil ; pull devil,
pull baker.” Push vessel, hold spasm ; hold spasm, push vessel. The vis medicatrix naturae brings on a spasm to remove the