Physiological Conceptions
Herman Boerhaave
In order to discover Truth in this manner by observation and reason, it is requisite we should fix on some principles whose certainty and effects are demonstrable to our senses, which may serve to explain the phenomena of natural bodies, and account for the accidents that arise in them; such only are those which are purely material in the human body, with mechanical and physical experiments; for we are not sensible of any other way of attaining to a true knowledge of the universal and particular affections of bodies.
Demonstration is an evident proof of some dubious proposition, so that nobody who admits the general principles, can deny their assent; these are purest in the mathematics, though there are many demonstrations no less evident in physic, especially those which are taken from anatomy. But there is no necessity for the principles of any art to be proved in that art, it is sufficient if their certainty is by any means demonstrated in other arts.
These ought to be first adjusted with distinction, clearness, and certainty; with distinction, which points out one being from any other; as if one was to define a circle to be a right line continued upon a point till one end meets again with the other; with clearness, which consists of simple notions or ideas, easily conceived by any man in his senses, as that two and two joined make four; with certainty, which cannot be denied by any reasonable person, or which must always appear true upon examination.
The universal laws of nature, or affections of all bodies, depend on mechanical and physical principles, upon which alone their actions are explicable; the same laws are also true in the human body, for its matter appears to be universally the same with that of all other bodies; so that what may be said to be true of all bodies, may be also affirmed true in our own. Thus, if one should affirm, that by the friction of two bodies would arise heat, the same will also be true upon the friction of solid parts in the human body. But then there are other principles not to be explained by these universal laws, but by some particular disposition in the certain body; these properties are called physical. But a physician ought to consider both the affections of bodies in general, as well as those only proper to the human body, that from a judicious comparison and just reasoning, he may never subject the human body to those laws only, to which the generality of, but not all, bodies are liable.
26. But as there are in the human body many other appearances not intelligible upon those principles, they therefore are not to be demonstrated and explained by such principles; if we would avoid error we must take a very different course for that purpose; this will readily appear to any one who considers and admits for true the following propositions, which are elsewhere demonstrated:
Such as memory, understanding, reason and the knowledge of past and future appearances; which are peculiar to the mind, a being without figure or extension, and conscious of pleasure and pain.
27. We are to consider (1) that Man is composed of a body and mind, united to each other; (2) that the nature of these are very different, and that therefore, (3) each has a life, actions and affections differing from the other; yet (4) that there is such a reciprocal connection and consent between the particular thoughts and affections of the mind and the body, that a change in one always produces a change in the other, and the reverse; also (5) that the mind performs some actions by mere thought, without any effect upon the body; and that it has other thoughts, which arise barely from some change in the condition of the body; on the other hand, also, (6) that there are some actions performed by the body without the attention, knowledge, or desire of the mind, which is neither concerned therein as the cause or effect of those actions; that there are also Some ideas formed in the mind of a person in health by its past actions; and, lastly, that there are other ideas compounded both of the past and present. That (7) whatever we observe to arise from thought in the human body, is to be only ascribed to the mind as the cause. But (8) that every appearance which has solidity, figure, or motion, is to be ascribed to the body and its motion for a principle, and ought to be demonstrated and explained by their properties. That (9) we cannot understand or explain the manner in which the body and mind reciprocally act upon each other from any consideration of their nature separate; we can only (10) remark by observation their effects upon each other, without explaining them, and when any difficulty or appearance has been traced so far, that it only remains to explain the manner of their reciprocal action, we are to suppose such account satisfactory, both because it may be sufficient for all the purposes of the physician, and as it is impossible for him to search any further.
By the body we understand that part of us which is extended in three dimensions, has a form, and is fitted for motion, or rest, etc.
By the mind we understand that being which thinks, and perceives itself thinking, and the thing thought of.
The union of the body and mind is such, that the mind cannot resist forming to itself the ideas of pleasure and pain, when the body is in a particular manner affected; nor can the healthy body refuse to obey the action of the mind under particular circumstances.
By the nature of the body or mind, we understand everything which we are satisfied belong to each. The essential nature of the mind is to be conscious, or to think; but to think of this and that particular thing, is accidental to it. The essential nature of the body is extension and resistance. These attributes have nothing in common to each other, nor ought one to conclude from similitude, that two beings are reducible to one general class. When I think of extension, it does hot infer anything of thought; and when I reflect upon thought, I can perceive no connexion of it with extension; therefore the idea of the body has nothing in common with that of the mind, and the reverse. In the same manner, there is no connexion between the common ideas of time, sound, gravity, light, etc. Socrates made a proper answer to Crito, when he was asked in what place he should choose to be buried? viz. "You will not find Socrates when you prepare my tomb, nor shall I be sensible of what you then do for me." Nor are the reasons wanting to prove from the present condition of the mind, that it may live hereafter without any commerce with its body.
The incomparable mathematician Vietus, who first restored algebra to us, received the enemies’ letters from the king, to expound their mystical signs; while he was studying to explain their meaning, he was taken up with the most profound meditation for three whole days and nights, insomuch that he was not sensible of what had been transacted without his knowledge, taking no more concern of his body, than if it had been long deserted as an enemy by his mind. In like manner, we find Archimedes in a consternation when he first was ordered to answer King Hiero concerning the mixed gold in the crown till at last lighting upon the experiment, i.e., going into the bath, he cried out victory. And in the same manner a Roman, who was in a deep consternation of ecstasy, being not at all terrified at the advances of the Syracutians in battle, made a great conquest without once breaking his lines.
The life of the body is, 1. To generate motion under particular circumstances, as the loadstone approaches to iron. 2. For its constituent parts to attract each other, from whence proceeds the resistance to the force of external bodies, or vis inertia. 3. To gravitate, or tend towards the center of its planet. And then, 4, comes the affections proper to particular bodies. The life of the mind is, 1. To perceive the appearances of all external objects, by the changes they make in the organs of sensation. 2. To judge or compare the nature of two ideas with each other, and then to deduce some consequences, as that they are of the same kind, or different; as we conclude from the notions of a circle and triangle, that a triangle is not a circle. 3. To will anything. In a word, the life of the mind is to be conscious. These are all the functions of the mind; for past actions are uncertain, and they may be all referred to the single act of its consciousness.
The action of the body is to communicate motion to other bodies; the passions of it is to receive some change in itself from another body or a mind. The action of the mind is volition, which everybody is acquainted with, but no one can explain. The passions of the mind are the changes it receives from external objects by the senses. Suppose the mind to be thinking of a circle, and in the interim a cannon to go off, it will lose the idea of a circle, and acquire that of sound; this is the sufferance of the mind, because it can neither retain the idea of a circle, nor resist that of sound. There are also some affections in the mind different from the preceding, such as violent passions, or involuntary commotions, which the mind cannot resist, and the faculty by which it moves and determines the several parts of the human body, agreeable to its inclination.
We cannot understand why two principles, which have no agreement in power, should thus concur in the same functions, though there have been three hypotheses framed to explain the intercourse of the body and mind; the first is, by the physical influx, which supposes the thing thought of, and the thought itself, to be one and the same; which we shall hereafter demonstrate to be absurd, inasmuch as our mind is ignorant of its own nature. The second is the system of occasional causes; and the third Supposes a harmony established by God, taking it for an infallible rule, that determinate actions of the mind must be necessarily attended with corresponding motions in the body, and the contrary; and this last seems to be the truest opinion, but it leaves us equally in the dark with the other.
If any action is to be explained which is compounded both of the faculties of the mind as well as of the body, such as walking, pain, voluntary respiration, etc., a just account ought to be first given how far, and in what manner, the body is concerned in the action, and then also of the mind; if this can be done, it is enough, without diving into the manner of connexion between the different actions; the explication of the corporeal actions’ appertains to the physician, and those of the mind to the philosopher; but their connexion can be explained by no man. Heat may be conceived to arise in bodies without any relation to a thinking mind, as millstones grow hot in their grinding; but motion is not explicable from the affections of the body, nor even from the properties of the mind; therefore heat and motion are not accountable from the mind; and if you should say that the voluntary motions of the muscles proceed from the act of volition in the mind, you explain the thing not in the least, because there is nothing in the idea of motion which is also to be found in any affection of the mind. We call an explanation of a thing the demonstration of agreement or relation between its own properties and the same in another; but this is here not only impossible, but also quite useless to a physician; for the great business of a physician is to be acquainted with the means of restoring lost health, and no cure can be affected by him, but through some change made in the human body by the application of others; therefore this search after the connexion between the body and mind not appertaining to a physician, is to be rejected, among those which are useless to the art. The physician, who cures diseases of the body, is not solicitous about those of the mind; for when the first is set to rights, the latter will quickly return to its office. Thus when the eye is blinded with a cataract, the mind cannot perceive sensible objects by it, the aid of physic is therefore called in to couch the cataract, or depress the opaque crystalline lens; after which the rays of light finding free admission to the retina, the mind will be sensible of visible objects by it; and thus the business of physic will be done without the assistance of optics. When a person is in a delirium, or swoon, the physician cannot recall the mind, which has no relation to his business; but by applying vinegar, or other volatiles to the nose, he can restore the sick machine to its former motions, and then the mind will also exhibit its former actions, and this full as well as if he understood the manner of connexion between the actions of the body and those of the conscious mind.