PART II.

ON THE PHYSIOLOGICAL RELATIONS OF SUGAR.

DIABETES MELLITUS consisting of an unusual flow of sugar from the body with the urine, the first step to be taken in an investigation of the nature of the disease, is to establish clearly, the natural or physiological relations of sugar in the animal economy. It will be readily conceded, I think, that a knowledge concerning the abnormal bearings of sugar in the economy, is not likely to rest upon any satisfactory footing, until a correct notion has been obtained of the state that is normal. It is only, I conceive, through physiology that we are in a position to approach advantageously the pathology of diabetes.

Willis, it appears, about the year 1674, was the first to discover that the urine in diabetes possessed a sweet taste, and it was left till a century later (1778) for Cowley to isolate the saccharine principle. Sugar was subsequently detected in the blood. Towards the close of the eighteenth century, Rollo promulgated the notion that diabetes was due to an imperfect digestion-to a derangement, having its seat in the stomach, and resulting from a peculiar alteration in the gastric juice, which had acquired the pretended morbid property of changing into sugar the vegetable materials ingested. Later, however, Tiedemann and Gmelin showed that during the digestion of amylaceous matter,

sugar was naturally formed in the intestine; and, Magendie and others, subsequently proved that sugar likewise passed into the blood, whilst the digestion of amylaceous matter was going forward. It hence followed, that the formation and absorption of sugar in the digestive system from vegetable materials, could no longer be looked upon as the source of diabetes, because such processes were shown to take place as physiological occurrences. Bernard's investi

gations were at this stage commenced, and as his views have lately formed the accredited doctrine upon this subject, and were the means of eliciting my own researches, I shall have to refer to them in detail as I proceed.

Looking to the extensive distribution of sugar in the vegetable kingdom, and to its entering so largely into the constitution of the food of animals, there can be no doubt that it forms an exceedingly important material, both in regard to animal and vegetable life. Being soluble, and of a highly diffusible character, it readily passes, after ingestion into the animal system, by a physical process, from the stomach and intestine into the circulation. The action of the blood-vessels, in respect to absorption, is purely physical; whilst the special absorbent system of the intestine, as it commences in the villi, has a peculiar selective power, picking up certain materials (oleo-albuminous), and rejecting others, in a manner that cannot be explained by physics. Sugar, salines, and such like, pass, in conformity with the laws of endosmose and exosmose, into the blood of the portal system, and are carried to the liver before entering the general circulation. Now, from facts I shall have to bring forward, it appears that sugar is arrested in the liver, and converted by it into a material, which is found pretty largely in the healthy organ.

Besides sugar itself, there is another material, even more extensively existing in the vegetable kingdom, which,

although presenting far different properties to sugar, yet is transformed into it with the greatest rapidity when certain conditions are present. This substance-starch-is of no use, I apprehend, as such, either to the animal or the plant. It would seem to form a store of carbonaceous material, which may be kept for centuries without undergoing change; but which, when exposed to the conditions leading to its requirement, is with rapidity transformed into sugar—a material that can be made use of in the processes belonging to active life. A grain of wheat, excavated with the mummy belonging to ages past, retains its starch unchanged. Supply this grain of wheat with warmth, air, and moisture, and active life commences. The starch now immediately begins to be transformed; the condition that has created a demand for it, leads to its transformation into a body, which is afterwards susceptible of being appropriated to the wants of the growing organism.

In vegetable life, it is diastase-a principle developed during germination- which occasions the metamorphosis of starch into dextrine and sugar. It seems to me exceedingly doubtful, however, if starch pass on from dextrine into sugar during germination to the extent that is generally imagined. Certainly, the quantity of sugar contained in malt must not be taken as an index of the quantity of sugar actually existing in the germinating grain. I have allowed barley to grow in a temperate atmosphere, fully to the extent that is done by the maltster; and, on making a cold infusion of it, have obtained an astonishingly slight indication of the presence of sugar. On the infusion being warmed, however, or on the growing barley being exposed to a moderately elevated temperature-as is done in malting, on the kiln-a large production of sugar is observed to result. What I have said, refers only to barley that has germinated to the extent allowed in malting; for, it is true that, without

the application of artificial heat, when barley has grown much beyond this extent, a considerable quantity of sugar will be found to be contained in it.

In the animal system, there are secretions poured out by the digestive apparatus, which have the power of rapidly transforming starch into sugar. Human saliva converts starch into sugar with an astonishing rapidity, but it is curious, that the saliva of all other animals does not possess a similar property. It is a fact that I can attest from my own experience, that the secretions collected from the large salivary glands of the dog, either taken separately or mixed together, have no action whatever towards converting starch into sugar. It appears, however, that the fluid derived from the mouth possesses, to a slight extent, a transformative power. But, that the saliva is not the fluid specially intended for acting upon the amylaceous constituents of our food, is to be inferred from other considerations, besides the difference just alluded to, in the extent of power it enjoys, amongst different members of the animal kingdom. is seldom ingested as food under such favorable circumstances for transformation, as it exists in our operations out of the body where a decoction is employed. The food is delayed but a comparatively short period of time in contact with the saliva in the mouth; and, supposing any action to take place in this cavity, it must be checked when the stomach is reached; for, it can be shown by experiment that our saliva exerts no transformative effect in the presence of an acid.

Starch

There is another secretion which is poured into the digestive tract further on, that seems to be specially intended for converting starch into sugar. The pancreatic juice at 90° to 100° rapidly occasions the conversion of starch into sugar; and, unlike what is the case with saliva, all the conditions in the interior of the system are favorable

for the exercise of its power. The food has been reduced to a semifluid state, so that it can become thoroughly incorporated with the secretions. The acid of the chyme has been more or less neutralized by the alkali of the pancreatic juice and bile. The temperature is elevated and equable; and, the passage along the intestine is slow, by which the starch is delayed in contact with its metamorphosing agent. Probably the secretion from Brunner's glands, and possibly that from the surface of the small intestine, assist the pancreatic juice, which, also has an office to perform in connection with the emulsification or preparation of fatty matters for absorption.

Such external sources of sugar, are all that were known previous to Bernard's time. Now, after an attentive examination of the circumstances connected with diabetes, Bernard was led to think that there might be something besides amylaceous matter-something unknown to chemists and physiologists, that might give rise to the production of sugar in the body. This, he particularly inferred from the fact, that the quantity of sugar escaping from a diabetic patient, under a mixed diet, was much greater than could be accounted for by the starch and sugar ingested; and that, although saccharine and amylaceous materials might be completely abstained from, still sugar did not cease to appear in the urine. Here was his motive for undertaking an investigation, out of which have sprung such unanticipated results.

In Bernard's first experiments, animals were kept upon a diet of a strongly saccharine character, with the view of ascertaining, how far the sugar could be followed in the circulatory system, after its absorption by the branches of the portal vein. His results led him to the conclusion that it might be detected as far as between the liver and the right side of the heart. To show that the sugar en