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CHAPTER V.

PATHOLOGY OF DIABETES.-CONDITION OF THE URINE:

POLYURIA, QUANTITY OF UREA.—AZOTURIA, GLUCOSURIA

OR MELLITURIA.

THERE is, sooner or later, in diabetes a great increase in the daily secretion of urine, or polyuria. The quantity voided in twenty-four hours is subject to considerable variation from a variety of causes, and ranges from four to forty pints. This excess is due to the presence in the blood of diabetic sugar, which has a strong attraction for water, and thus produces a powerfully diuretic effect. The larger the quantity of sugar elaborated by the disease and circulating in the blood in a given period the greater the polyuria; hence the quantity of urine voided is regulated by the nature of the diet and the severity and stage of the disease: conditions which determine the amount of diabetic sugar produced in any given

case.

Nearly the whole of the water drunk by diabetics

passes off by the kidneys, a small portion only being excreted by the lungs; and, as already stated, the excessive discharge of urine excites intense thirst, and is thus compensated for by the quantity of fluid drunk. In many instances, however, the discharge of urine is so enormous as to have given rise to the supposition that it is in excess of the quantity of fluid drunk. This opinion, although believed in by several recent authorities of distinction, is, as I have already pointed out, as ancient as the times of Celsus and Aræteus. To account for this phenomenon it has been supposed that, either water is absorbed by the skin and lungs or is formed in the body, or that the latter loses weight.

The belief in such a phenomenon, if it did not originate in, has most probably been perpetuated by, a source of fallacy, caused by the singular fact that water is often retained in the body in diabetes for a considerable period; so that if an observation is limited to a single day, more urine may be passed on that particular day than the drink consumed; this circumstance being due to a portion of the water drunk on the previous day being then discharged as urine. But if observations to determine this question extend over a sufficiently lengthened period-from eight to twelve days-so as to exclude this source of

fallacy, very different results are obtained. Thus Dr. Parkes quotes the experiments of Nasse, Von Dursch, Rosenstein, and others, and refers to his own, in addition, to demonstrate that the quantity of fluid taken surpasses the amount of urine voided and the fluid excreted by the lungs included. We may therefore conclude,' he observes, that at present there is no reason to think either that water is absorbed or formed in the body. Occasionally, no doubt, the body may for a time lose more water than it receives; it will then lose weight.'1

It has been proved by the experiments of Falck,2 confirmed by those of Griesenger and Neuschler, that the water drunk by diabetics is not passed so rapidly by the urine as in healthy persons. Thus if a certain quantity of drink is taken in the morning, there may be no increase of the urine until mid-day, but if an equal quantity is taken by a healthy person at the same period, the maximum discharge of urine will be shortly after. In other words, the elimination of water is retarded in diabetics, and for the same reason the excretion of urine is regular. Falck attempted to explain this fact by attributing it

1 Op. cit. p. 34.

'Deutsche Klinik, 1853, and Vogel in Canstatt's Jahresb. 1853. Report on Chronic Diseases.

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to a retarded absorption from the stomach. But Professor Vogel, of Halle, has offered an explanation which is certainly more satisfactory and more philosophical, being founded on certain physical conditions created by the presence of sugar in the blood, and the alteration in density to which the latter is thereby subjected. 'When,' says Professor Vogel, a diabetic is deprived of drink for a certain period, his blood becomes more concentrated in consequence of the urinary secretion which continues. This concentrated blood, much richer in solid materials than normal blood, forcibly attracts the water of the parenchymatous fluids (extra-vascular) until the degree of concentration of the latter is in equilibrium with the serum. But when the healthy individual drinks a considerable quantity of fluid, the water absorbed rapidly augments the quantity of the blood, and consequently the intra-vascular pressure; diuresis immediately follows, and ceases as soon as the greater part of the water absorbed is thereby removed. But when a diabetic drinks the same quantity of liquid, the effect is quite different, even when the gastric absorption is as rapid in the one case as in the other. The blood is diluted by the water absorbed, but the

1 Krankheiten der harnbereitenden Organe. (Virchow's Handbuch der Pathologie. Erlangen, 1863.)

parenchymatous liquids, rich in sugar, are much more concentrated in the diabetic than in the healthy subject; they by exosmotic attraction withdraw from the blood serum a part of the absorbed water, so that immediately after the ingestion of liquid the diuresis is less abundant than in a healthy person. But in proportion as the blood, in consequence of the urinary excretion, attains a higher degree of concentration, it takes back in its turn from the parenchymatous liquids the water it had given them, so that more slowly, when a considerable interval has passed since the ingestion of drink, the diuresis is relatively more abundant with diabetics than in healthy persons.'

There can be no doubt that the modified osmotic changes described in this explanation are, in diabetes, continually in operation between the blood serum and the extra-vascular tissue fluids, and are caused by the saccharine impregnation of the blood, which in its turn produces a similar saccharine condition of these tissue fluids. The augmented specific gravity of the blood serum, in the first instance, increases the activity of the endosmotic process, so that a large quantity of fluid at once passes from the tissues into the blood-vessels, and thirst is thus excited, to be allayed by drinking. By the com