function of the organ. This has been specially the case in some of the ductless or endocrine glands, which manufacture chemical bodies called hormones, which enter the blood-vessels in the glands and so reach and influence other parts of the body. Thomas Addison, of Guy's Hospital, found that a certain group of symptoms-pigmentation of the skin, gastric disturbance, and great muscular and heart weakness-were associated with disease of the adrenal glands. The publication, in 1855, of his account of this condition, now called Addison's disease, stimulated physiologists, especially Brown-Séquard, to investigate the use of the adrenal glands which, in 1894, were shown by Schäfer and Oliver to provide an internal secretion-adrenalin or epinephrin-with the power of contracting and toning up the blood-vessels. This substance has been made synthetically and is much used in medical practice. Disease of the thyroid gland in the neck, and its complete removal by the surgeon for goitre, were found to give rise to certain symptoms called myxedema or cachexia strumipriva respectively, and these observations again drew attention to the need for investigation of the uses of the gland in health, and of the composition of the internal secretion which it pours into the circulation to act as a tonic or stimulus to tissue changes; in other words, it increases metabolism. These researches, though not yet completed, have provided results of the greatest importance to national health, especially in areas where goitre -in this country so-called Derbyshire neck-is common. The thyroid gland is specially concerned with the control and supply of iodine in the body, just as small glands in its neighbourhood, the parathyroids, look after the metabolism of calcium. When there is a deficiency of iodine the thyroid enlarges and may eventually form a goitre; this can be prevented by giving small doses of iodine, and as a result of the adoption of this plan the frequency of goitre in children in Switzerland and in the neighbourhood of the Great Lakes in North America has been most notably diminished at a very small cost of money or time. It may be added that, while the reasoning which led up to this important piece of preventive medicine was being collected, assistance was gained by observation of goitres in trout in America

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ecia and their dependence on deficiency of iodine. This is ada 1 an example of the value of comparative pathology, a zes, i means of advancing medicine which is rightly being increasingly employed; thus at Cambridge there is an institute for research in comparative pathology, a subject on the importance of which Sir Clifford Allbutt had consistently insisted since 1888, and which he happily lived to see adopted by the University in which he had been Regius Professor of Physic for the long period of thirty-two years.

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It has long been known that the pancreas which pours an external secretion into the intestine to digest starches, changing them into sugar as well as taking a prominent part in the changes necessary for the absorption of fats and protein substances such as meat, also has an internal secretion which passes into the blood and controls the metabolism of sugar absorbed from the intestines. In 1869, Langerhans described in the pancreas the cellular structures known as the islands of Langerhans; these provide the internal secretion of the gland which is now known as insulin; destruction or disease of these islands causes a deficiency of insulin and so diabetes mellitus. In 1921 an extract of these islands was prepared in a satisfactory form for use in the human subject by Dr F. G. Banting, working at Torontọ with the help of Prof. J. J. R. MacLeod; this preparation, insulin, when injected under the skin of a patient with diabetes, supplies the absent hormone, as the internal secretion is also called, necessary to enable the body to make use of the sugar in his circulation; in other words, by this substitution treatment the diabetic patient becomes more or less normal for a few hours. The effect, however, is transient, so that the injections have to be repeated, and it has not been proved that a permanent cure can be obtained by the injection of insulin. When the internal secretion of the thyroid gland is absent the extract of the gland, or its active principal thyroxin, must be constantly supplied artificially in order to keep off the effects (called myxedema) of its absence, and the same is true in the case of diabetes mellitus and insulin. The beneficial effects of the insulin treatment in saving and prolonging life can admit of no possible doubt whatever; but, like other remedies

powerful for good, it may be given unsuitably and do harm; its administration, therefore, requires skilled medical supervision.

Disease of the pituitary gland may produce remarkable changes in growth; many of the giants who get a living in shows are examples of acromegaly which is due to disease of this gland of internal secretion; another form of bodily change due to disease of this gland of internal secretion is a special form of obesity, such as was depicted by Charles Dickens in the fat boy 'Joe' in 'Pickwick.'

The application of the pure sciences to medicine has been a feature of the last hundred years, and many examples could be brought forward from biology, chemistry, physics, and mathematics. A brief reference has been already made to biochemistry, and it need hardly be said that the problems of digestion, diabetes, renal disease, and metabolism in general depend largely on organic chemistry. Ophthalmic practice, perhaps the nearest approach to an exact science in medicine, owes much to the laws of physics; thus the fitting of appropriate spectacles for errors of refraction depends on a knowledge of laws of optics. The ophthalmoscope, originally invented by Charles Babbage and modified by Helmholtz, permits the interior of the eye, which may be regarded as an extension of the brain, to be inspected so that the condition of the blood-vessels and of the retina can be examined; its application to medicine was initiated less than sixty years ago by Hughlings Jackson, a most philosophical neurologist, and by Sir Clifford Allbutt, who, in the year of Babbage's death (1871), brought out his classical monograph, The Use of the Ophthalmoscope in Diseases of the Nervous System and of the Kidneys, and also in certain General Diseases,' the first really comprehensive review of the application of this instrument of precision as a means of diagnosis in clinical medicine. Sir Clifford Allbutt also invented the present form of clinical thermometer, which is so familiar that comparatively few of those who day in day out use it know to whom they are indebted for this convenient instrument.

After bacteriology, which is a branch of biology, no advance has been of such signal service to the practice

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of medicine and surgery as the introduction of X-rays. Discovered almost accidentally by Prof. W. K. von Röntgen, of Würzburg, in December 1895, when working with an electrically excited Crookes tube, X-rays provided a means of seeing the position and state of substances opaque to X-rays in the human body; thus a bullet or a broken bone can be localised, and in the thirty years that have elapsed since this discovery the technique of X-rays has been greatly improved and their scope of usefulness widely extended. For instance, the first X-ray photograph, or skiagram, taken in this country, on Jan. 16, 1896, by Mr Campbell Swinton, occupied twenty minutes; whereas, in 1921, Dr Robert Knox took one-also of the hand-in one-hundredth of a second. First employed for purposes of surgical diagnosis, such as the localisation of a needle in the hand, the position of a swallowed coin, or the presence of a stone in the kidney, they were soon employed for the detection of disease inside the chest, such as an aneurysm or tuberculosis of the lungs. Radiography is now used in any doubtful case of abdominal disease; as salts of bismuth and barium are opaque to X-rays and therefore cast a shadow on the X-rays screen or plate, comparatively large quantities of bismuth or barium salts are swallowed, and behaving like an insoluble meal, their progress through the stomach and intestines can be watched; and so any delay in the passage of the bismuth meal, such as might be due to a narrowing of the intestine, can be detected. Its use has also been extended to the head for detection of tumours, and of disease of the roots of the teeth which are embedded in the jaws, and thus a frequent cause of chronic inflammation of the joints can be detected when to the eye there is not any evidence of dental poisoning. Although Röntgen rays are used in various ways for the treatment and cure of disease, their outstanding addition to the practice of medicine has been in diagnosis, for a completely new method of examination has thus been provided. Radium, which possesses rays of the same nature, has also been extensively used for its local destructive action on new growths, especially for superficial cancer of the skin, and has been most successful in the form on the face known as rodent ulcer. It may be

noted that, like other remedies powerful for good, X-rays and radium may do harm when employed in excess; the early workers in the branch of medicine suffered severely from exposure to X-rays before their harmful effects were known, and it is now well recognised that cancer may result from repeated exposures and that the blood may be seriously affected, a very grave form of anæmia developing.

Medical statistics originating in the work of John Graunt and Sir William Petty (1662) were really brought into being by Dr William Farr (1807-83), who from 1838 to 1879 was compiler of statistics at the RegistrarGeneral's Office; Prof. Karl Pearson's efforts have started a school of expert Medical Statisticians. A slightly junior contemporary of Farr was Sir John Simon (18161904), the first Medical Officer of the City of London (1848), of the General Board of Health (1855-58), and of the Privy Council under the Public Health Act (1858-71); he had a great share in the rise of preventive medicine and the study of epidemics. The outbreaks of cholera in this country, in 1831, 1849, and 1853, led to the appointment of Commissions and to administrative sanitary reform; the Local Government Board was created in 1871, and after the Great War was expanded into the Ministry of Health. Coincidentally with the reforms thus instituted in the sanitary conditions the standardised rate of mortality has fallen nearly 20 per cent. since 1870, and the average expectation of life for every individual in London has risen by twenty years since 1841.

With the rapid advance of knowledge due to new methods, especially of technique, medicine has become too extensive for one mind to cover, and as a result some limitation of the scope of activities in a medical man's practice is inevitable. Specialism has come to stay, and the days of the encyclopædists and Admirable Crichtons have passed, though it is undesirable to return to the days of ancient Egypt when each disease was undertaken by one man who did not concern himself with any other complaint. Specialism is, therefore, no new thing; but there is the danger of its being overdone, and too narrow a view may result from intensive study of one organ of the body if undertaken so early that there has not been time to acquire a good perspective of the ills that flesh