Hydrophilia

HYDROPHILIA, HYDROPHILICITY (from the Greek hydor-water and philia-love), the ability to bind water. In biology and medicine, hydrophilia is judged by the amount of water bound by tissues—by the so-called "non-free water" of tissues (see Edema); it cannot be used for urination, other types of secretion, or for circulatory fluids (blood, lymph). The concept of "Oedembereitschaft," the readiness of tissues for edema, partially corresponds to hydrophilia. One should distinguish between the hydrophilia of the organism as a whole, i.e., the total amount of water that can be bound depending on a whole range of conditions (for example, on the retention of salts in tissues, which sharply lowers the amount of "free water"), and the specific, most frequently used meaning of hydrophilia as the degree of hydrophilicity of tissue colloids, their ability to swell and to bind water. The majority of colloids that make up animal and plant organisms belong to the group of hydrophilic substances, i.e., those that greedily bind water. Corresponding to various theories of the genesis of edema, individual authors put forward different factors that determine the hydrophilia of biocolloids. According to Loeb, hydrophilia corresponds to the osmotic pressure of the tissue; according to M. Fischer, it corresponds to the concentration of H-ions. Insufficient gas exchange in the tissue, leading to its acidosis, increases the adsorption capacity with respect to water. Besides acidity, i.e., the concentration of H-ions, hydrophilia is also regulated by other cations and anions. The weak point of Fischer's doctrine, which is based on the observation of the swelling of biocolloids in various solutions and on experiments on the swelling of necrotic or necrobiotic objects, is the preoccupation with only one side of the complex processes regulating the hydration of tissues. Schade, on the contrary, attributes to H-ions the ability to lower the hydrophilia of tissues in the organism and puts forward the decisive importance of the oncotic pressure of tissues for hydrophilia. The latter, according to some authors, is the osmotic pressure of proteins, the physiological significance of which was noted by Starling; Schade, however, understands oncotic pressure as the adsorption properties of colloids with respect to water. It depends on the ratio of various proteins in the tissue; thus, albumins bind water more strongly than globulins. Hydrophilia, accordingly, represents the sum of the osmotic and oncotic properties of the tissue. The character of tissue lipoids exerts an influence on hydrophilia. Mayer and Schaeffer discovered that the ability to bind water in a mixture of proteins with lipoids increases with an increase in cholesterol content; hydrophilia, thus, is directly proportional to the cholesterol-to-lipocytic coefficient (fatty acids).

According to Terroine, an analogous coefficient of the content of lipoids in the blood (lipemic) corresponds to the lipocytic coefficient of tissues: knowing it, one can judge the hydrophilia of tissues. In 1923, Aldrich and McClure proposed a skin test for clinical judgment of hydrophilia: 0.2 cubic centimeters of physiological NaCl solution is injected into the thickness of the skin of the forearm; in healthy individuals, the edema from the injection is resorbed slowly (50-90 minutes); resorption is accelerated during pathological increases in hydrophilia.