the origin and nature of the morbid process, or diseased action, by which the food is converted into sugar, we encounter great obscurity and uncertainty.

or not.

Although a minute trace of sugar appears to be present in healthy blood, it cannot be considered to be a normal constituent of the latter in appreciable quantity. For a long period it was doubted whether sugar is actually present in the blood in diabetes, This doubt arose partly from the defective methods of analysis then in use, and partly to the presence of sugar being obscured by the various constituents of the blood. Diabetic sugar was first detected in the blood in 1835, by Ambrosiani of Milan, who separated it in small quantity and in the form of crystals, together with a larger proportion of uncrystallisable and fermentable syrup; the form of analysis employed was of a complicated nature. Shortly afterwards it was detected by Dr. Charles Maitland.' The investigations of Ambrosiani and Dr. Maitland were subsequently confirmed by the researches of Dr. McGregor of Glasgow, and since that period numerous researches have established beyond doubt that the blood in diabetes is impregnated with sugar.

1 London Med. Gazette, vol. xvii. p. 900.
2 Ibid. May 13 and 20, 1837, vol. xx.

I

The quantity of sugar found in the blood in diabetes is small, a fact which is readily accounted for by its strong affinity for water, by which it is rapidly cast out of the blood by the kidneys. The proportion of sugar found in 1,000 parts of diabetic blood is shown by the following analyses :

Dr. Pavy states that he has made several examinations of diabetic blood removed by cupping and venesection, and has found it to contain sufficient sugar to produce a copious orange-yellow reduction with the copper solution. On one occasion he made a quantitative analysis of a specimen of blood abstracted from the loins by cupping, and found the sugar present in it to amount to 53-100ths, or slightly more than half a grain per cent., or to about two and a half grains to the fluid ounce.

The existence of diabetic sugar in the blood in ponderable quantity having been established, it is necessary to consider the more important and plausible hypotheses which have from time to time been advanced to account for its origin and presence in this fluid.

1

The first theory which claims attention may be termed the gastric; it was advanced by Rollo near the end of the last century; he expressed the opinion that diabetes is produced by derangement of the function of digestion, and is confined chiefly to the stomach. According to him the disease consists in 'an increased action and secretion, with a vitiation of the gastric juice,' which acquires a morbid property of converting the vegetable portions of the food ingested into sugar. This hypothesis, however, became untenable on the discovery by Tiedemann and Gmelin that during digestion starchy matter is converted into sugar as a healthy process; and still more so when it was ascertained, by Magendie and other investigators, that during the digestion of starch the blood of the vena porta becomes charged with sugar.

Mr. McGregor also advocated the gastric origin of diabetes in a modified form. By a series of experiments he discovered that sugar is present in the stomach and intestines of diabetics after the ingestion of animal food alone, from which sugar is not produced during digestion in healthy persons. This fact he ascertained by giving an emetic and purgative to a diabetic, to clean out the alimentary canal,

1 On Diabetes, Mellitus, London, 1797.

and then feeding him on roast beef and water exclusively for a period of three days, at the end of which he obtained the contents of the stomach by an emetic of sulphate of zinc, and found that they fermented briskly, thus revealing the presence of a considerable quantity of sugar. The same experiment performed on a healthy person, on the contrary, yielded only negative results. Mr. McGregor of course found sugar in the stomach of healthy persons after the digestion of starchy food, but in much smaller quantity than in those suffering from diabetes.

The conclusions drawn from these experiments were: first, that in diabetes sugar is formed in excess; and, secondly, that the sugar thus formed, instead of undergoing further changes in the progress of assimilation, is imported into the blood, where it remains unchanged until it is eliminated by the kidneys. This arrest of the assimilation of sugar was attributed to deficient or exhausted influence of the nerves supplying the assimilating viscera and vascular system.

6

Dr. Prout1 expressed the opinion, that diabetes is nothing more nor less than a form of dyspepsia; that this dyspepsia principally consists in a difficulty

1 Op. cit. p. 38.

of assimilating the saccharine alimentary principle, and that, like all other forms of dyspepsia, whether it be an inherited or an induced affection, diabetes is liable to be much modified and aggravated by concomitant circumstances.'

With regard to Mr. McGregor's hypothesis, it must be observed that the presence of sugar in the stomach of a diabetic fed exclusively on animal food does not by any means prove that it was formed there during digestion. It has been already pointed out in the preceding pages, that after the blood has become thoroughly impregnated with sugar, the tissue fluids in their turn become saturated with it also; and so also do most of the secretions, and amongst them the gastric juice in particular. In this manner its presence in the stomach may readily be accounted for.

So much for the theories as to the gastric origin and nature of diabetes; it is necessary next to consider the hypotheses which have been advanced concerning its hepatic origin, or supposed seat in the liver.

Sugar when taken into the stomach is, on account of its solubility and highly diffusible nature, immediately absorbed into the circulating current by the blood-vessels in obedience to the laws of osmosis.