Hydrophilia

HYDROPHILIA, HYDROPHILICITY (from Greek hydor-water and philia-love), the ability to bind water. In biology and medicine, hydrophilia is judged by the amount of water that can be bound by tissues—by the so-called 'non-free water' of tissues (see Edema); it cannot be used for urination, other forms of secretion, or for circulating fluids (blood, lymph). In part, hydrophilia corresponds to the concept 'Oedembereitschaft', the readiness of tissues to develop edema. 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 number of conditions (for example, the retention of salts in tissues, which sharply reduces the amount of 'free water'), and the particular, most commonly used meaning of hydrophilia as the degree of hydrophilicity of tissue colloids, their ability to swell and bind water. Most colloids that make up animal and plant organisms belong to the hydrophilic group, i.e., those that avidly bind water. Corresponding to different theories of the genesis of edema, various authors put forward different factors determining the hydrophilia of biocolloids. According to Loeb, hydrophilia corresponds to the osmotic pressure of the tissue, according to M. Fischer—to the concentration of H-ions. Insufficient gas exchange in the tissue, leading to its acidosis, increases the adsorptive capacity with respect to water. In addition to acidity, i.e., the concentration of H-ions, hydrophilia is also regulated by other cations and anions. A weakness in Fischer's teaching, based on observations of the swelling of biocolloids in various solutions and on experiments with edema of necrotic or necrobiotic objects, is the fascination with only one side of the complex processes regulating tissue hydration. Scha-de, on the contrary, attributes to H-ions the ability to lower the hydrophilia of tissues in the body and assigns decisive importance to 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; Scha-de, however, understands oncotic pressure as the adsorptive properties of colloids with respect to water. It depends on the ratio of different 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 nature of tissue lipoids affects 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 is thus directly proportional to the cholesterol-lipocytic coefficient of _{fatty acids}. According to Terroine, a similar coefficient of lipoid content 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 cm of physiological NaCl solution is injected into the thickness of the forearm skin; in healthy individuals, the edema from the injection dissipates slowly (50-90 minutes); dissipation is accelerated with pathological increases in hydrophilia.