OBESITY - ETIOLOGY.
The main constituents of the human body by whose deposition and transformation it is built up and maintained are, aside from in organic salts and ingredients of the ash, albumin, fat, and water.
Of these three constituents albumin and water are present in the normal organism in a proportionate quantity which does not vary materially ; the former amounts to 15 or 16 per cent. of the weight of the body, while the latter varies only between 58.5 and 65.7 per cent.
(Moleschott), except after an abundant ingestion of fluid, when the blood and the tissues temporarily contain more water.
The fat alone, even in the healthy body, exists in such a variable quantity that the limits are wide apart and can only approximately be determined as ranging between 9 and 23 per cent. of the body weight. The total amount in general is also apt to be greater in wo men than in men, the proportion being as 16 to 13.5 per cent. Be sides, within the limits of health the quantity of fat which is to be considered as normal varies according to the age, constitution, occu pation, family tendency, season, climate, and racial peculiarities.
The use of the fat in the body is due to its chemical and physical properties.
The fat, being inclosed in vesicles whose membrane, saturated with water, can bear strong pressure without allowing the oily con tents to escape, forms in its physical quality a thick elastic layer on the surface of the body, fills up interspaces and depressions between organs, bones, ligaments and muscles, protects against blows and other mechanical injuries, and contributes to the physical beauty of the body. Being a bad conductor of heat it furthermore protects the tissues which it covers and envelops against refrigeration; this ap plies not only to the panniculus adiposus with reference to the sur face of the body, but also to the fatty omentum with regard to the intestine which is so sensitive to changes of temperature. Lean per sons and old people whose fat is partly consumed are therefore more sensitive to a fall of the external temperature than others who are shielded by an ample layer of adipose tissue.
In a chemico-physiological relation fat serves iu the animal econ omy by its combustion for the production of force and heat and thus prevents waste of albumin in metabolism. These qualities impart to fat a considerable influence on general nutrition and the physiological functions, and we shall have to study them carefully with reference to excessive formation and accumulation of fat, as well as to the at tempt to reduce the amount of this substance in the body.
The fat in the body is formed by cellular elements from the lipo genous material, fat and carbohydrates, which reaches the blood by way of nutrition and is supplied to them. Decomposition products of albumin can likewise be changed into fat. The fat cell per ,se is capable of considerable metabolism. The fat formed in the fat cells may sooner or later be again decomposed, whereby diffusible sub stances develop which pass through the cells and are absorbed by the blood. When the state of nutrition is good this process probably takes place constantly, so that the same fat does not remain for years in the cells, but is ever decomposed and re-formed: The fat which has become superfluous is inclosed in the body at the points of its formation in the fat cells ; these, being fastened to gether by connective tissue, represent the adipose tissue. Regarding the origin of the adipose tissue two different theories have been ad vanced by histologists. • According to Toldt adipose tissue occurs in the body preformed as a normal tissue formation; it does not exist everywhere, but is lack ing in the eyelids, auricles, scrotum, penis, clitoris, nymphm, also in the muscular connective tissue of the intestine, etc. At these points, even under the most favorable conditions for fat formation, no ap preciable deposition of fat occurs. At other points, however, both on the surface and in the interior, there are thick layers of this tissue in which according to circumstances large quantities of fat are accu mulated. These points are, on the external parts of the body, the malar region of the face, the panniculus adiposus of the breast, the an terior abdominal wall, the pubic region, the sole of the foot, the ischial cushion, the lower and upper extremities. In the thoracic and abdominal cavities fatty tissue exists in the mediastinum, the epicardium, the surface of the heart, the mesentery, the greater omen tum, in the appendices epiploicu, the adipose capsule of the kidneys, and finally also in the intermuscular tissue of the voluntary muscles and the yellow bone marrow.