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The question as to whether the study of normal phenomena should or should not precede the study of abnormal ones, is of the greatest importance; and a neglect of it has introduced confusion into every work I have seen on general or comparative history. For this preliminary being unsettled, there has been no recognized principle of arrangement; and historians, instead of following a scientific method suited to the actual exigencies of our knowledge, have adopted an empirical method suited to their own exigencies; and have given priority to different countries, sometimes according to their size, sometimes according to their antiquity, sometimes according to their geographical position, sometimes according to their wealth, sometimes according to their religion, sometimes according to the brilliancy of their literature, and sometimes according to the facilities which the historian himself possessed for collecting materials. All these are factitious considerations; and, in a philosophic view, it is evident that precedence should be given to countries by the historian solely in reference to the ease with which their history can be generalized; following in this respect the scientific plan of proceeding from the simple to the complex. This leads us to the conclusion that, in the study of Man, as in the study of Nature, the question of priority resolves itself into a question of aberration; and that the more aberrant any people have been, that is to say, the more they have been interfered with, the lower they must be placed in an arrangement of the history of various countries. Coleridge (Lit. Remains, vol. i. p. 326, and elsewhere in his works) seems to suppose that the order should be the reverse of what I have stated, and that the laws both of mind and body can be generalized from pathological data. Without wishing to express myself too positively in opposition to so profound a thinker as Coleridge, I cannot help saying that this is contradicted by an immense amount of evidence, and, so far as I am aware, is supported by none. It is contradicted by the fact, that those branches of inquiry which deal with phenomena little affected by foreign causes, have been raised to sciences sooner than those which deal with phenomena greatly affected by foreign causes. The organic world, for example, is more perturbed by the inorganic world, than the inorganic world is perturbed by it. Hence we find that the inorganic sciences have always been cultivated before the organic ones, and at the present moment are far more advanced than they. In the same way, human physiology is older than human pathology; and while the physiology of the vegetable kingdom has been successfully prosecuted since the latter half of the seventeenth century, the pathology of the vegetable kingdom can scarcely be said to exist, since none of its laws have been generalized, and no systematic researches, on a large scale, have yet been made into the morbid anatomy of plants. It appears, therefore, that different ages and different sciences bear unconscious testimony to the uselessness of paying much attention to the abnormal, until considerable progress has been made in the study of the normal; and this conclusion might be confirmed by innumerable authorities, who, differing from Coleridge, hold that physiology is the basis of pathology, and that the laws of disease are to be raised, not from the phenomena presented in disease, but from those presented in health; in other words, that pathology should be investigated deductively rather than inductively, and that morbid anatomy and clinical observations may verify the conclusions of science, but can never supply the means of creating the science itself. On this extremely interesting question, compare Geoffroy Saint-Hilaire, Hist. des Anomalies de l'Organisation, vol. ii. pp. 9, 10, 127; Bowman's Surgery, in Encyclop. of the Medical Sciences, p. 824; Bichat, Anatomie Générale, vol. i. p. 20; Cullen's Works, vol. i. p. 424; Comte, Philos. Positive, vol. iii. pp. 334, 335; Robin et Verdeil, Chimie Anatomique, vol. i. p. 68; Esquirol, Maladies Mentales, vol. i. p. 111; Georget, de la Folie, pp. 2, 391, 392; Brodie's Pathology and Surgery, p. 3; Blainville, Physiologie comparée, vol. i. p. 20; Feuchtersleben's Medical Psychology, p. 200; Lawrence's Lectures on Man, 1844, p. 45; Simon's Pathology, p. 5.
Another confirmation of the accuracy of this view is, that pathological investigations of the nervous system, numerous as they have been, have effected scarcely anything; the reason evidently being, that the preliminary knowledge of the normal state is not sufficiently advanced. See Noble on the Brain, pp. 76–92, 337, 338; Henry on the Nervous System, in Third Report of Brit. Assoc. p. 78; Holland's Medical Notes, p. 608; Jones and Sieveking's Patholog. Anat. p. 211.