His notes were subjected to perpetual revisions and additions.
Those who work with living forms of which it is possible to obtain a large number of specimens, and those who make revisions of the provisional species of palaeontologists, are slowly coming to some such conception as that a species is the abstract central point around which a group of variations oscillate, and that the peripheral oscillations of one species may even overlap those of an allied species.
Trans., 3rd ed., Edinburgh, 1854), and the Philosophic de Locke (4th ed., 1861) were simply matured revisions of his lectures during the period from 1815 to 1820.
Besides the attainments mentioned above, in respect of operative progress, many important revisions of older rule-of-thumb knowledge have come about, and not a few other substantial discoveries.
Among the revisions may be adduced some addition to our knowledge of dyspepsia, attained by analytic investigations into the contents of the stomach at various stages of digestion, and by examining the passage of opaque substances through the primae vine by the Rntgen rays.