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Rh their propagation of children. But bodily defect is largely a result of evil circumstances, in the prevention of which the physician is not unsuccessfully engaged, and the growth of sympathy means a stronger cement of the social structure. At any rate the mean standard of health will be raised, perhaps enormously.

In the tropics, as well as in Europe, such methods and such researches threw new light upon the causes and paths of the terrible infections of these climates. In 1880, two years before Koch discovered the bacillus of tubercle, C. L. A. Laveran (b. 1845) discovered the parasite of malaria, and truly conceived its relations to the disease; thus within two years were made two discoveries either of which was sufficient to make the honour of a century. Before the end of the 19th century this discovery of the blood parasite of malaria was crowned by the hypothesis of Patrick Manson, proved by Ronald Ross, that malaria is propagated by a certain genus of gnat, which acts as an intermediate host of the parasite. Cholera (Haffkine) and yellow fever are yielding up their secrets, and falling under some control. The 20th century, by means of this illumination of one of the darkest regions of disease, may diminish human suffering enormously, and may make habitable rich and beautiful regions of the earth’s surface now, so far as man’s work is concerned, condemned to sterility. Moreover, freedom of trade and of travel has been promoted by a reform of the antiquated, cumbrous, and too often futile methods of quarantine—a reform as yet very far from complete, but founded upon a better understanding of the nature and propagation of disease.

Special Departments.—Hitherto we have presented a survey of the progress of the science and practice of medicine on general lines; it remains to give some indication of the advance of these subjects of study and practice in particular departments. As regards infections, it is not to be supposed that our knowledge of these maladies has been advanced

by pathology and bacteriology only. In the clinical field also it has received a great enlargement. Diphtheria, long no doubt a plague among mankind, was not carefully described until by Pierre Bretonneau in 1826; and since his time our conception of this disease has been extended by the study of later, secondary and incidental phases of it, such as neuritis, which had always formed part of the diphtheritic series, though the connexion had not been detected. Influenza, again, was well known to us in 1836–1840, yet clinical observers had not traced out those sequels which, in the form of neuritis and mental disorder, have impressed upon our minds the persistent virulence of this infection, and the manifold forms of its activity. By the discovery of the bacillus of tubercle, the physician has been enabled to piece together a long and varied list of maladies under several names, such as scrofula and lupus, many of them long suspected to be tuberculous, but now known to belong to the series. It is on clinical grounds that beriberi, scarlet fever, measles, &c., are recognized as belonging to the same class, and evolving in phases which differ not in intimate nature but in the more superficial and inessential characters of time, rate and polymorphism; and the impression is gaining strength that acute rheumatism belongs to the group of the infections, certain sore throats, chorea and other apparently distinct maladies being terms of this series. Thus the field of disease arising not from essential defect in the body, but from external contingencies, is vastly enlarging; while on the other hand the great variability of individuals in susceptibility explains the very variable results of such extrinsic causes. Coincidently therewith, the hope of neutralizing infections by fortifying individual immunity has grown brighter, for it appears that immunity is not a very radical character, but one which, as in the case of vaccination, admits of modification and accurate adjustment in the individual, in no long time and by no very tedious methods. Evidence is accumulating which may end in the explanation and perhaps in the prevention of the direst of human woes—cancer itself, though at present inquiry is being directed rather to intrinsic than to extrinsic causes.

When, leaving the infections, we look for evidence of progress

in our knowledge of more or less local diseases, we may begin with the nervous system. It is in this department, from its abstruseness and complexity, that we should expect the advance of anatomy and physiology—normal and morbid—to be most delayed. If we consult the medical works

even of the middle of the 19th century we shall find that, in the light of the present time, accurate knowledge in this sphere, whether clinical, pathological or therapeutical, could scarcely be said to exist. Even in the hands of J. A. Lockhart Clarke (1817–1880), one of the earliest investigators of nervous pathology, the improvement of the compound microscope had not attained the achromatism, the penetration and the magnification which have since enabled J. L. C. Schroeder-van der Kolk (1797–1862), Albert von Kölliker, Santiago Ramon y Cajal, C. Golgi (b. 1844) and others to reveal the minute anatomy of the nervous centres; while the discrimination of tissues and morbid products by stains, as in the silver and osmic acid methods, and in those known by the names of Carl Weigert or Marchi, had scarcely begun. In England the Hospital for the Paralysed and Epileptic was founded in 1859, where Charles E. Brown-Séquard (1817–1894), J. Hughlings-Jackson, Thomas Buzzard, Henry C. Bastian (b. 1837), Sir W. R. Gowers and David Ferrier (b. 1843) found an adequate field for the clinical and pathological parts of their work. In France, in the wards of the Hôtel Dieu, Guillaume Benjamin Duchenne (1806–1875), in association with Trousseau and in his private clinic, pursued his memorable clinical and therapeutical researches into the diseases of the nervous system; and Jean M. Charcot (1825–1893) in that great asylum for the wreckage of humanity—the Salpêtrière—discovered an unworked mine of chronic nervous disease. M. H. Romberg (1795–1873) and Theodor Meynert (1833–1892) also were pioneers in the study of nervous diseases, but it was not till later in the century that Germany took a high place in this department of medicine. The discoveries of the separate paths of sensory and motor impulses in the spinal cord, and consequently of the laws of reflex action, by Charles Bell and Marshall Hall respectively, in their illumination of the phenomena of nervous function, may be compared with the discovery in the region of the vascular system of the circulation of the blood; for therein a key to large classes of normal and aberrant functions and a fertile principle of interpretation were obtained. Nor was the theory of reflex action confined to the more “mechanical” functions. By G. H. Lewes and others the doctrine of “cerebral reflex” was suggested, whereby actions, at first achieved only by incessant attention, became organized as conscious or subconscious habits; as for instance in the playing on musical or other instruments, when acts even of a very elaborate kind may directly follow the impulses of sensations, conscious adaptation and the deliberate choice of means being thus economized. This law has important ethical and political bearings; but in the province of disease this advance of what may be compared to the interlocking of points and signals has had wide influence not only in altering our conceptions of disease, but also in enlarging our views of all perturbations of function. The grouping of reflex “units,” and the paths wherein impulses travel and become associated, have been made out by the physiologist (Sherrington and others) working on the healthy animal, as well as by the record of disease; and not of spontaneous disease alone, for the artificial institution of morbid processes in animals has led to many of these discoveries, as in the method of A. V. Waller (1816–1870), who tracked the line of nervous strands by experimental sections, and showed that when particular strands are cut off from their nutritive centres the consequent degeneration follows the line of the separated strands. By similar methods nature, unassisted, betrays herself but too often; in many instances—probably originating primarily in the nervous tissues themselves—the course of disease is observed to follow certain paths with remarkable consistency, as for instance in diseases of particular tracts of the spinal cord. In such cases the paths of degeneration are so neatly defined that, when the tissues are prepared after death by modern methods, they are plainly to be seen running along certain columns, the subdivisions