XX. That most learned commentator upon Discorides, Andrew de Laguna, says, that if it could conveniently be done, it would be good policy to send those flaming young physicians, who are just come from the university, brimful of the bragadocio arrogance of _ergo_ and _probo_, to practise physic in those nations we are at war with, for that it would be attended with a great saving, both of men and money, to our own country. XXI. I can with confidence affirm, that there is no art or faculty, that can be less conducive to the acquisition of medicinal knowledge, than the physics of the schools. If all the philosophers that are, or ever were in the world, could be convened together, and remain in consultation for a hundred years, they would not in all that time, by the mere help of philosophical speculations, be able to instruct us how we should cure a chilblain; nor from that tumultuous consultation, should we obtain any maxim, that ought not to be prohibited as contraband, and refused admittance into the chamber of a sick person. Good sense joined to experience, either acquired by a man’s own, or the practice of other reputable people, are both the father and mother of medicinal knowledge; nor has physics, that is to say the physics of the schools, the least share in the propagation of this species. XXII. The reasoning of naturalists upon all kinds of mixtures, consists, in whether they are constituted of matter and substantial forms according to the doctrine of Aristotle, or of atoms according to that of Epicurus, or of salt, sulphur, and mercury, according to that of the chymists, or of the three elements, according to that of the Cartesians: whether these are composed of undivisible points, or of parts dividable _in infinitum_; whether their action or operation is from their texture, or the motion of their particles, or from some accidental virtues which they call qualities; whether these qualities are of the manifest or the occult kind; and whether they are of the first, second, or third class or species. Now what has all this to do with medicine? I will venture to pronounce no more, or rather less, than it has with geometry or jurisprudence. When a physician goes about to cure a tertian ague, all this farrago of questions applied to the operations or effect of the bark, is of no sort of use to him. The only thing that is of any importance for him to know, is, whether his experience has taught him, that in the present state of the disorder, it will be proper to administer this febrifuge; but this he is to infer, not from the maxims, _dici de omni, dici de nullo_; but from conviction, drawn from experiments he has made himself of its efficacy in the like cases, and also from those, which have been made by physicians of eminence who have wrote on the subject.