Dehydration

DEHYDRATION, loss by the organism of significant quantities of water, including that which enters into the composition of tissue colloids. Depending on the degree, dehydration manifests through a series of clinical symptoms, ranging from a general state of weakness to the most severe intoxication and even death. The latter occurs when the organism loses 10% of its contained water. Dehydration occurs primarily in a number of pathological conditions characterized by acute loss of large quantities of liquid in the form of diarrhea (cholera, cholera infantum, intestinal dyspepsia, etc.), during polyuria and prolonged or intense fever in acute infectious diseases. It is also observed in conditions accompanied by severe exhaustion, especially in the initial period of these diseases, when tissues show a tendency to lose water or are unable to bind it. In these cases, dehydration forms the basis of significant and rapid loss in weight (see also Fasting, Edematous Disease, Cachexia). Dehydration, however, can also occur in healthy people, especially in infants, with a sharp violation of their nutritional conditions. Reduction of the amount of liquid introduced into the organism to 40-50% of the normal amount while maintaining ordinary nutrition, especially with food rich in protein, leads to the onset of dehydration. In the blood, this results in significant thickening and decrease in the volume of circulating blood (oligemic hypovolemia), and clinically, general symptoms of severe intoxication, such as: drowsiness, apathy, and general restlessness, sinking of the eyeballs, dryness of the oral mucosa, rapid increase in pulse and respiration, to which is sometimes added fever of a non-infectious nature. Similar symptoms can also be observed experimentally in animals, and dehydration here is apparently only the initial cause of the intoxication, which is subsequently based on disturbance of protein metabolism and in particular the detoxifying (deaminating) role of the liver (see Liver, pathological physiology); obviously the severe childhood toxicoses associated with nutritional disturbances (see Exsiccoses), being largely caused by dehydration, represent from a pathophysiological standpoint an extremely complex disturbance of metabolism (protein, mineral, and water), in which dehydration plays the role of a precipitating factor.

m. entirely. Dehydration-drying, removal of water from a substance, is achieved by various methods, depending on the nature of the substance to be dehydrated, the required degree of dehydration, the strength of water binding by the given compound, and the convenience of execution. Some substances can be dehydrated by drying in a thin layer in the air or in a stream of air over water-removing substances (H₂SO₄, KOH, P₂O₅) in a regular or vacuum desiccator at ordinary, i.e., atmospheric, or reduced pressure; substances that permit heating are dried in drying ovens. For dehydration of organic liquids, various substances are used, for example, calcined copper sulfate, anhydrous calcium chloride, sodium sulfate, etc. To obtain anhydrous (absolute) alcohol, one can use shaking with calcined copper sulfate, treatment with quicklime followed by distillation, treatment with metallic sodium, and even better-calcium. To free ether from water, it is steeped with calcined CaCl₂, then with metallic Na (until cessation of hydrogen bubble evolution), and then distilled. For drying gases, they are passed through water-removing substances, for example, through concentrated H₂SO₄, P₂O₅, KOH, soda lime. Dehydration should be distinguished from dehydration-removal of water from the molecule of a chemical compound itself.

i. ovaries. In microscopic technique, dehydration aims to prepare a piece of tissue for microscopic examination by embedding it in celloidin or paraffin; on the other hand, a prepared and stained section is dehydrated to make it possible to mount it in Canadian balsam. The most commonly used medium for dehydration is alcohol, which also fixes and defats the tissues; the latter circumstance is an important factor in staining the preparation. For dehydration of a piece before embedding in celloidin or paraffin (after preliminary fixation with formalin or other fixing fluids), it is passed through the so-called alcohol battery, i.e., through a series of jars with alcohols of increasing strength (70-80-95-100°). The piece is kept in each alcohol for at least one day. For accelerated embedding, pieces can be kept for only a few hours (3-5), and small pieces for an even shorter time, and dehydration can be performed in an incubator at 37°. When embedding in celloidin, the piece from 100° alcohol is transferred to a mixture of absolute alcohol and ether aa, and for paraffin embedding-to a mixture of 100° alcohol with xylene or other hydrocarbons, chloroform (see Histological Technique). The absolute alcohol necessary for dehydration is prepared as follows: crushed copper sulfate is calcined in a crucible until it, by loss of water, takes the form of a white powder, which is then poured into a bottle with alcohol. Anhydrous copper sulfate removes water from the alcohol, turning blue again. This method can also be used to test the purity of absolute alcohol: calcined white copper sulfate should not turn blue in it. For dehydration of ether, the procedure is the same as for dehydration of alcohol. Dehydration is started immediately with 100° alcohol in cases (where it also serves as a fixative) when the substance required for staining, for example glycogen, dissolves in aqueous fixatives. Besides dehydration, alcohol also defats the tissues, therefore in staining fat (with Sudan III or scarlet red) it should not be used. When it is necessary to perform rapid dehydration of a piece, acetone can be used, which fixes and dehydrates small pieces within 30 minutes; the disadvantage of acetone dehydration is its wrinkling effect on tissues. Rapid fixation and dehydration without wrinkling is achieved with Carnoy's (Carneau's) mixture (absolute alcohol-6 parts, glacial acetic acid-1 part, chloroform-3 parts), into which a small piece is placed for 1-2 hours, after which it is placed in absolute alcohol for 2-3 hours. For dehydration of celloidin sections, a mixture of absolute alcohol and chloroform aa is used, but it is better to use, as with dehydration of paraffin sections, two changes of 95° alcohol. In cases where alcohol extracts aniline dyes and damages the preparation, it is necessary to perform dehydration of sections as quickly as possible. If the preparation is overstained, aniline oil can be added to the alcohol to extract the aniline dye. For dehydration of thin sections stained with complex aniline dyes (for example, in staining granules), it is recommended to dehydrate sections with pure acetone. From alcohol, sections are transferred to a clearing medium-various essential oils (see Histological Technique), in which alcohol and any remaining water are extracted. Then the section is washed in xylene and mounted on a slide in balsam.