Page:EB1911 - Volume 18.djvu/215

 functional disturbances affect the general nutrition of the body they have been termed Metabolic Diseases (Stoffwechselkrankheiten). It is impossible to draw a hard and fast line between functional and organic disease, since the one passes gradually into the other, as is well seen in gout. Nor is it always easy to decide how far the conditions are due merely to quantitative alterations in the metabolism and how far to actual qualitative changes, for it is highly probable that many of the apparently qualitative alterations are 'really quantitative disturbances in one part of the protoplasmic mechanism, leading to an apparent qualitative change in the total result of the activity.

Obesity.—It is as fat that the surplus food absorbed is stored in the body; but the power of storing fat varies enormously in different individuals, and in some it may be considered pathological. The reasons of this are very imperfectly understood. One undoubted cause of obesity is taking a supply of food in excess of the energy requirements of the individual. The amount of food may be absolutely large, or large relatively to the muscular energy evolved in mechanical work or in heat-production; but in either case, when fat begins to be deposited, the muscular activity of the body tends to diminish and the loss of heat from the surface is reduced; and thus the energy requirements become less, and a smaller diet is sufficient to yield the surplus for further storage of fat. Fat is formed from carbohydrates, and possibly indirectly from proteids (see ). Individuals probably vary in their mode of dealing with these substances, some having the tendency. to convert them to fat, some to burn them off at once. Carl von Noorden, however, who has studied the metabolism in cases of obesity, finds no marked departure from the normal. It may be that in some persons there is a very perfect absorption of food, but so far no scientific evidence for this view is forthcoming. In all cases the fat stored is available as a source of energy, and this circumstance is taken advantage of in the various fat “cures,” which consist in giving a diet containing enough proteids to cover the requirements of the body, with a supply of fats and carbohydrates insufficient to meet the energy requirements of the individual. This is illustrated by the dietaries of some of the best known of these “cures”:—

In a normal individual in moderate muscular activity about 3000 Calories per diem are required (see ), and therefore under the diets of these “cures,” especially when accompanied by a proper amount of muscular exercise, the fats stored in the body are rapidly used up.

Diabetes, as distinguished from transitory glycosuria, is produced by a diminution in the power of the tissues to use sugar, which thus accumulates in the blood and escapes in the urine. One great source of energy being unavailable, the tissues have to use more fats and more proteids to procure the necessary energy, and hence, unless these are supplied in very large quantities, there is a tendency to emaciation.

The power of storing and using sugar in the tissues is strictly limited, and varies considerably in healthy individuals. Normally, when about 200 grms. of glucose are taken at one time, some of it appears in the urine within one hour. In some individuals the taking of even 100 grms. leads to a transient glycosuria, while others can take 250 grms. or more and use it all. But even in the same healthy individual the power of using sugar varies at different times and in different conditions, muscular exercise markedly increasing the combustion. Again, some sugars are more readily used than others, and therefore have a less tendency to appear in the urine when taken in the food. Milk-sugar and laevulose appear in the urine more readily than glucose. This power of using sugar possessed by an individual may depend to a small extent on the capacity of the liver to store as glycogen any excess of carbohydrates absorbed from the food, and some slight cases of transient glycosuria may be accounted for by a diminution of this capacity. But the typical form of diabetes cannot be thus explained. It has been maintained that increased production of sugar is a cause of some cases of the disease, and this view has been supported by Claude Bernard’s classical experiment of producing glycosuria by puncturing the floor of the fourth ventricle in the brain of the rabbit. But after such puncture the glycosuria occurs only when glycogen is present in the liver. It is transient and has nothing to do with true diabetes. The fact that various toxic substances, e.g. carbon monoxide, produce glycosuria has been used as an argument in support of this view, but they too seem to act by causing a conversion of glycogen to glucose, and are effective only when the liver is charged with the former substance. At one time it was thought that the occurrence of glycosuria under the administration of phloridzin proved that diabetes is due to a poison. But the fact that, while sugar appears abundantly in the urine under phloridzin, it is not increased in the blood, shows that the drug acts not by diminishing the power of the tissues to use sugar, but by increasing the excretion of sugar through the kidneys and thus causing its loss to the body. Hence the tissues have to fall back upon the proteids, and an increased excretion of nitrogen is produced. This, however, is a totally different condition from diabetes.

Anything which produces a marked diminution in the normally limited power of the tissues to use sugar will cause the disease in a lighter or graver form. As age advances the activity of the various metabolic processes may diminish irregularly in certain individuals, and it is possible that the loss of the power of using sugar may be sooner impaired in some than in others, and thus diabetes be produced. But Minkowski and von Mering have demonstrated, by experiments upon animals, that pathological changes in the pancreas have probably a causal relationship with the disease. They found that excision of that organ in dogs, &c., produced all the symptoms of diabetes—the appearances of sugar in the urine, its increased amount in the blood, the rapid breaking-down of proteids, and the resulting emaciation and azoturia. At the same time the absorption from the intestine of proteids, fats and carbohydrates was diminished. How this pancreatic diabetes is produced has not been explained; 'It has been suggested that the pancreas forms an internal secretion which stimulates the utilization of sugar in the tissues. Though in a certain number of cases of diabetes disease of the pancreas has been found, other cases are recorded where grave disease of that organ has not produced this condition. But the apparent extent of a lesion is often no measure of the depth to which the functions of the structure in which it is situated are altered, and it is very possible that the functions of the pancreas may in many cases be profoundly modified without our methods of research being able to detect the change. The pancreas consists of two parts, the secreting structure and the epithelial islets, and one or other of these may be more specially involved, and thus alteration in digestion and absorption on the one hand, and changes in the utilization of carbohydrates on the other, may be separately produced. The subcutaneous injection of large doses of extracts of the supra-renal bodies causes glycosuria and an increase of sugar in the blood, but the relationship of this condition to diabetes has not yet been investigated.

The disease may be divided into two forms:—

1. Slight Cases.—The individual can use small quantities of sugar, but the taking of larger amounts causes glycosuria. Supposing that the energy requirements of an individual are met by a diet of— then if only 100 grms. of glucose can be used, the energy value of 300 grms., i.e. 1230 Calories, must be supplied from proteids and fats. To yield this, 300 grms. of proteids or 132 grms. of fats would be required. If these are not forthcoming in the diet, they must