element is most abundant in the coats of the smaller and ultimate ramifications of the arterial system, such as occur in the white substance of the brain, medulla, and spinal cord, the middle coat, indeed, of these arteries being purely muscular. It follows, therefore, that any degree of atrophy of this muscular structure must give rise to the dilatation of these vessels.

That the capillaries and veins do not share in the morbid process described by Dr. Dickinson can readily be accounted for by the peculiar structure of their walls. The capillaries are destitute of muscular structure, and consist everywhere of a single delicate structureless coat, while the veins of the white and grey substance of the brain and spinal cord, according to the authority of Kölliker,1 contain not a trace of muscular fibre. Besides, the capillaries and veins are beyond the distending systolic force of the heart's action.

That a failure of nutrition analogous to that found in the brain and cord by Dr. Dickinson does not occur in any other organ in diabetes may be accounted for by the peculiarity of the relation between the arteries and nervous tissue. It is well known that the external elastic coat (tunica adven

1 Manual of Microscopic Human Anatomy. London, 1860, p. 242.

titia) of connective areolar tissue, intervening as a cushion between the arteries and the tissues of most of the organs of the body, is absent in the substance of the brain and spinal cord: the arteries in these organs being surrounded by a homogeneous envelope in close contact with the nerve tissue, which is consequently not shielded from the influence of the pressure exerted by the dilated arteries, this pressure producing the atrophy observed only along the course of their distribution.

If this explanation should be correct, it would follow that the phenomena described by Dr. Dickinson are the effect and not the cause of diabetes.

To sum up, it will appear, from the preceding observations, that neither clinical observation nor experimental research have as yet revealed the real nature of diabetes: which, therefore, must still be regarded as a disease of obscure and uncertain origin.

The Etiology of diabetes is certainly not less obscure than the nature of the morbid process constituting the disease. It has, in turn, been attributed to a great variety of causes, none of which, however, can be said to have been traced, with any degree of precision, as capable of generally exciting it. Intemperance, dissipation, sexual

excess, mental emotions, and the like influences. have been considered capable of producing the malady; but if such causes exercised any important influence in exciting it, diabetes would be, certainly, of more frequent occurrence. So far as my

own observation goes, I have not seen it more frequently amongst the intemperate than in those of the most regular and careful habits. The disease occurs to the robust as well as to those of delicate constitution, to every variety of temperament, and to both sexes of every age, after childhood, during which period of life, however, it is but seldom observed. It does not appear to depend on any peculiar kind of food, nor to be influenced by climate, as has been asserted by several writers.

Diabetes is, indeed, considered as an hereditary 'affection, and undoubtedly it is to a certain extent, but by no means to the same degree as most other diseases known to have an hereditary transmission. Those who have an hereditary tendency to it are generally of a scrofulous or tubercular diathesis.

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CHAPTER VIII.

PATHOLOGY OF DIABETES-PROGRESS AND DURATION; COMPLICATIONS: PULMONARY PHTHISIS, CONGESTION OF THE LUNGS, PNEUMONIA AND BRONCHITIS; CARBUNCLES, MALIGNANT BOILS, AND DIFFUSE INFLAMMATION OF THE SUBCUTANEOUS AREOLAR TISSUE; GANGRENE; DERANGEMENTS OF VISION.

DIABETES is a disease of indefinite duration; its progress being modified by a variety of conditions, such as age, idiosyncrasy, diet, and regimen: but more especially the invasion of incidental or secondary affections to which it gives a proclivity, or of which it determines the development.

The disease, as a very general rule, progresses much more rapidly towards a fatal termination in young subjects below the age of maturity, and even in those below the age of thirty or thirty-five years, than in persons at or beyond the middle period of life, after which its intensity becomes greatly diminished. Consequently, in elderly people, its pro

gress is generally tardy, so that, occasionally, it never advances beyond the first stage, and continues so mild as not seriously to impair health.

The grave character of the malady in early life is well illustrated by Dr. Prout,1 who states that in his extensive experience of thirty-five years, and embracing nearly seven hundred cases, he witnessed twelve instances of diabetes in young subjects between the ages of eight and twenty years, not one of whom reached the age of maturity; the greater proportion dying in various ways after a short course of the disease. Professor Christison has informed me that his experience as to the fatal character of the affection in youth is not of a more favourable description.

The fact that diabetes is very rarely recognised at its very commencement, owing to the insidious nature of its invasion, renders it extremely difficult to form an approximation even to a correct estimate of its duration in the vast majority of instances. According to the researches of Griesinger,2 who has given an analysis of 225 cases, it would appear that the average duration of the disease is from two to three years. Dr. Prout states that out

1 Op. cit. p. 36.

2 Archiv. für physiologische Heilkunde, Jahrg. 1859.