Eighteenth-century nosology and its survivors.

IT IS well known that Sydenham recommended classifying diseases 'with the same care which we see exhibited by botanists in their phytologies'.1 He suggested elsewhere that attempts to discover the causes of diseases were doomed to fail,2 man's faculties being shaped 'to perceive only the superficies of bodies, not the minute processes in nature's "abyss of cause" '. It is thus man's duty to confine himself and not to venture beyond the natural limitations of his cognition. For only the physician who submits to this duty can hope to be of real service to mankind and not get caught in a web of 'curious and irrelevant speculations."' John Locke (1632-1704), Sydenham's friend and, like him, a physician, supported the plea for self-imposed restraint. 'The learned men of former ages', he writes, 'employed a great part of their time and thoughts searching out the hidden causes of distemper, were curious in imagining the secret workmanship of nature and ... putting all these fancies together, fashioned themselves systems and hypotheses', which have 'diverted their enquiries from the knowledge of things'.5 There can be no hope of progress if medicine continues on the same path. Locke concludes that 'we are so far from being capable of 'knowing the causes and mechanisms of natural phenomena that it is 'lost labour to seek after it'.6 For 'pouring and gazing on the parts which we dissect without perceiving the very precise way of their working is but still a superficial knowledge, and though we cut into these inside, we see but the outside of things and make but a new superficies for ourselves to stare at'.7 Not even with the help of a microscope can we hope to pass beyond the natural limitations of our cognition. 'What microscope, however exquisitely elaborate, shall make visible those minute pores by which, for example, the chyle passes from the intestines to the chyliferous vessels? Or what microscope shall exhibit those ducts through which the blood, conducted by the arteries, is passed onwards to the orifices of the veins?' Sydenham asks.8 And even if any one had 'so sharp a knife and sight', Locke adds, 'as to ... make an ocular demonstration that the pores of the parenchyma of the liver or kidneys were either round or square and that the parts of urine and gall separated in these parts were a size and figure answerable to those pores. I …