Galenism suffered especially from logical systematization, and the system of van Helmont, while far less orderly, also had its own basic principles on which all else depended. Boyle, however, practiced medicine on a thoroughly different basis. He did not depend on system or logic. In the words that Hunter used to Jenner over a hundred years later, other physicians would think the answers to their problems. Boyle, however, preferred to try the experiment. He wanted facts.
But this attitude, which sounds so modern, so praiseworthy and enlightened, had one serious flaw. What was a fact? And how did you know? This important problem, so significant for the growth of scientific medicine, we can study quite readily in the works of Robert Boyle.
The problem, in a sense, resolves around the notion of credulity. What shall we believe? Boyle makes some distinctions between what he has seen with his own eyes and what other people report to have seen. Thus, he mentions "a very experienced and sober gentleman, who is much talked of" who cured cancer of the female breast "by the outward application of an indolent powder, some of which he also gave me." But, he adds cautiously, he has not yet "had the opportunity to make trial of it."[52] Clearly, since he cannot make the trial himself, Boyle withholds judgment, even though the material came from a "very experienced" gentleman. Or again, he talks about "sober travelers" who made certain claims regarding the treatment of poisons. But, he says, "having not yet made any trial of this my self, I dare not build upon it."[53]
There are numerous such instances, scattered throughout his works, where he reports an alleged cure but specifically indicates his own mental reservations. Clearly, he is quite cautious in accepting the statements of others, even though they were "sober" or "experienced" or even "judicious." On the other hand, he is extremely uncritical when he himself uses the term "cure" and when he attributes cures to particular medicines.
His skepticism he indicates in references, for example, to Paracelsus and van Helmont. Their specific remedy against "the stone," he says, and their claims that they can reduce stones to "insipid water, is so strange (not to say incredible) that their followers must pardon me, if I be not forward to believe such unlikely things, til sufficient experience hath convinced me of their truth."[54] Here, of course, we see further a feature of critical acumen. A claim is made, but if this claim runs counter to Boyle's own accepted body of knowledge, or to logical doctrines derived from other directions, mere assertion cannot carry conviction. "Sufficient experience" must play its part, and just what constitutes "sufficient" we are not quite sure.
In judging the effectiveness of a remedy or the credibility of a statement, one of the most important weapons was analogy. Direct observation of a phenomenon was good. Next best was direct observation of some analogous phenomenon whereby one body acted upon another to alter its properties or induce significant changes. Boyle drew his analogies largely from chemistry, but he had no hesitation in applying them to medicine.
Claims that medicines swallowed by mouth could dissolve stones in the bladder seemed a priori unlikely. Yet there was considerable authority that this took place; many persons had reported that this was a fact. Boyle kept an open mind. He might be highly skeptical in regard to the claims for any particular medication, but he did not deny the principle involved. The possibility that some fluid, when swallowed, could have a particular specific action on stones in the bladder, without affecting the rest of the body, he considered quite plausible through the analogy that quicksilver has an affinity with gold but has no effect upon iron. Furthermore, a substance than can corrode a solid body may nevertheless be unable to "fret" a different body which is considerably softer and thinner, if the "texture" does not admit the small particles.[55] Reasoning by analogy served to explain the logical plausibility. In other words, he was very open-minded. He refused to dismiss all such claims, and provided analogy as a reason for keeping his mind open; yet he refused to accept particular claims of medicine that dissolved stones, because the evidence was not convincing. We could scarcely ask for more.
An important seventeenth-century medical document was the report of Sir Kenelm Digby, regarding the so-called "weapon salve." The essay describing this famous powder was written in 1657, and I have discussed it at some length elsewhere.[56] Here again Boyle keeps an open mind, saying, "and if there be any truth in what hath been affirmed to me by several eye-witnesses, as well physicians as others, concerning the weapon-salve, and powder of sympathy, we may well conclude, that nature may perform divers cures, for which the help of chirurgery is wont to be implored, with much less pain to the patient, than the chirurgeon is wont to put him to."[57]
One great advantage of chemistry, thought Boyle, lay in the help it provided in investigating the materia medica. Chemistry, he thought, could help to purify many of the inorganic medicines and make them safer, without impairing their medicinal properties. Furthermore, chemistry could help investigate various medications customarily employed in medicine, where "there hath not yet been sufficient proof given of their having any medical virtues at all."[58] Boyle believed that by proper chemical analysis he could isolate active components, or, contrariwise, by failing to extract any valuable component, he could eliminate that medicine from use. While a major interest, perhaps, was a desire to provide inexpensive medicines, he was well aware that much of what went into prescriptions probably had no value. Furthermore, he felt that his chemical analysis could indicate whether value and merit were present or not.
The same skepticism applies to remedies that, far from being expensive, were common and yet rather disgusting. The use of feces and urine as medication was widespread. The medical virtues of human urine represent, he believed, a topic far too great to be considered in a brief compass. But he declared that he knew an "ancient gentlewoman" suffering from various "chronical distempers" who every morning drank her own urine, "by the use of which she strangely recovered."[59] Boyle was quite skeptical of the reports of others, which he had not had opportunity to try himself. But in therapeutic trials that he himself had witnessed, he seemed utterly convinced that the medication in question was responsible for the cure and was quite content to accept the evidence of a single case.