Gelatin

GELATIN (Gelatina alba), or animal (white) glue, is obtained by prolonged boiling of collagenous tissue (bones, tendons, skin, cartilage, etc.). Commercial gelatin has the appearance of colorless or whitish transparent thin sheets, with a glass-like luster, odorless and almost tasteless. In cold water, it swells significantly without dissolving, while in hot water it dissolves easily and completely, forming a sticky, transparent or slightly opalescent liquid, which upon cooling solidifies into a jelly-like mass. Aqueous solutions easily undergo putrefaction. Gelatin is insoluble in ethyl alcohol and ether. An aqueous solution of gelatin rotates the plane of polarization to the left. Gelatin consists almost entirely of glutin; upon hydrolysis, it yields a series of amino compounds. In the digestive tract, gelatin is altered in such a way that the resulting products are partially absorbed. In the body, gelatin is oxidized more easily and therefore utilized more quickly than complete proteins, which gelatin, as a plastic substance, cannot fully replace in a normal diet. However, in the formation of connective tissue elements, primarily the skeleton, gelatin plays a significant plastic role. The final products of gelatin metabolism in the body are urea, CO₂, and H₂O. When taken internally, gelatin limits putrefactive processes in the intestine and serves as a protection for its mucous membrane. Of particular value are the hemostatic properties of gelatin, which manifest both upon direct contact with bleeding surfaces and through general (resorptive) action. The mechanism of hemostasis is not yet known with precision. Dastre and Floresco (1896) hypothesized that gelatin increases blood coagulability and agglutinates erythrocytes due to its calcium content (up to 0.6%) and, perhaps, some other components. According to Gley and Richet, pure and dialyzed gelatin loses this property. Spagnoli (1926), in experiments on animals after intravenous injection of gelatin, observed leukopenia, which he considers the result of leukocyte destruction, leading to an enhancement of the blood's coagulating properties. Gelatin is used in therapy for various types of non-surgical hemorrhages (pulmonary, gastric, renal, uterine, intestinal) and hemorrhagic diathesis (hemophilia, purpura haemorrhagica, morbus Werlhofi), as well as (now rarely) for aortic aneurysm. Furthermore, gelatin serves as a base for suppositories and other dosage forms, for the preparation of capsules, solid culture media for bacteria, etc. Solutions for injection must be thoroughly sterilized, as gelatin often contains tetanus bacilli spores. Solutions are sterilized in saturated water vapor, as in dry heat or in saline solution at 115° in an autoclave, the solutions are destroyed. Sterility is verified by injection into guinea pigs. Sterile gelatin intended for injection—Gelatina sterilisata—is manufactured by the firm E. Merck. Before use, solidified gelatin solutions are gently warmed (in hot water) until they return to a liquid state. Gelatin is chemically incompatible (causing precipitation) with metal salts, mineral acids, alcohol, and tannins. In bacteriological practice, gelatin is used by adding it in amounts of 10–15% to nutrient broths for the preparation of solid media for cultures. Preparations. 1. Gelatina alba (Pharmacopoeia of the USSR)—locally, a 5–10% sterile solution (compress) on the bleeding site; internally, 1 tablespoon of a 5–10% solution (up to 4–6 grams or more per day); in an enema, 50–100 cm³ of a 10% solution; subcutaneously, from 15 to 200 cm³ of a 2–5% (according to other authors, 20–50 cm³ of a 10%) solution in physiological saline. 2. Gelatina sterilisata pro injectione (Merck)—a reliably sterilized 10% gelatin solution; subcutaneously, 5–10–40 cm³; internally, 2 tablespoons 3 times a day. 3. Gelatina Zinci—a glue paste that liquefies when warm and solidifies on the skin into an elastic mass. Its composition is as follows: Zinci oxydati crudi 10.0, Gelatinae albae 15.0, Glycerini 40.0, Aq. dest. 35.0, M. f. pastam. DS. Heat, apply to the skin (wound), and then cover with cotton wool and a starch bandage. Besides this, there are other gelatin pastes (Gelatinae "Unna")—with salicylic acid (5–20%), camphor (5%), chloral hydrate (10%), etc. Gelatin with glycerin serves as the base for Kaloderma—a popular cosmetic product.

M. Nikolaev. Gelatin in histological technique is used in the manufacture of injection masses, for embedding histological objects for the purpose of cutting them on a microtome, and as a medium for mounting sections and other microscopic objects. A. For mounting, a mixture of gelatin with glycerin (so-called glycerin-gelatin) is usually used, which is prepared in various ways, for example, by the Kaiser method (7 g of gelatin is soaked for 2 hours in 42 g of distilled water, 50 g of glycerin and 1 g of carbolic acid are added, heated while stirring for 10-15 minutes, and filtered through moistened glass wool). The refractive index of glycerin-gelatin is 1.447. Mounting objects in glycerin-gelatin is performed directly from water and is used in cases where it is necessary to avoid passing objects through alcohol, for example, in the case of staining them with dyes that are easily soluble in alcohol. B. Embedding in gelatin is performed in cases where it is necessary to protect the object from the action of alcohol to avoid shrinkage and especially the dissolution of fat. With this method, even the most fragile objects do not crumble, such as, for example, eggs rich in yolk. When embedding objects in gelatin for which heating to 60° is indifferent, the Apathy method is used; where high temperature might be harmful, for example, when examining for fat and lipoids, the Gaskell-Graif method is resorted to. 1. Apathy method. 50 g of gelatin (dry, in sheets or powder) is dissolved in a heated mixture of 175 g of distilled water and 25 g of glycerin, filtered in a thermostat, and dried in it under CaCl₂. A viscous mass is obtained, which is cut into cubes and stored in a sealed vessel. Objects hardened in 96° alcohol are gradually transferred to a mixture of glycerin (4 parts) and water (5 parts), to which an even solution of gelatin (3 parts of the prepared mass in 7 parts of warm water) is then added. In the latter, the pieces remain for 24 hours at 40°, then they are transferred together with the gelatin mixture into a thermostat (45-60°) and the mixture is allowed to evaporate to half its volume, after which it is allowed to solidify at room temperature, cut into pieces 5-6 mm thick, and gradually passed through absolute alcohol (5-6 days) into terpineol (5-6 days), after which they can be cut. This method allows avoiding any shrinkage. 2. Gaskell-Graif method. A first liquid and a second thick gelatin solution are prepared. The latter is prepared by dissolving 3 weight parts of gelatin in 3 weight parts of 1% carbolic water at 37° in a closed vessel. The first is prepared by diluting 1 part of the thick solution with 1 part of carbolic water. Fixed pieces of tissue 3 mm thick are washed for 24 hours with water and placed for 3-24 hours first in liquid, and then for the same amount of time in thick gelatin at 37°, after which the mass with the piece is transferred to an icebox and then dried in the air to the consistency of rubber. After this, it is transferred for 1-2 days into a formalin solution (1:4). Before cutting, the blocks are washed for 1/2 hour in water. Cutting can be done on a freezing microtome (10 μ) or on a sliding one, for which the pieces are glued to a wooden block with a thick gelatin solution, hardened for 24 hours in a formalin solution (1:4), and cut, wetting with 30% alcohol. G. Epstein. Nutrient gelatin, a solid nutrient medium used for growing microorganisms; introduced into bacteriological practice by R. Koch. It is prepared from meat water or Liebig's extract and ordinary commercial gelatin used for culinary purposes. Method of preparing nutrient gelatin: to 1 liter of meat water or a 10% solution of Liebig's extract, add 10 g of peptone, 5 g of NaCl, and 100-150 g of gelatin cut into small pieces. Instead of meat water, one can use ready-made broth, adding the appropriate amount of gelatin to it. After the gelatin swells, the mixture is heated until dissolved in a water bath at 40-50° (no higher, to avoid coagulation of proteins), then a neutral or slightly alkaline reaction is established (by litmus) by adding a saturated solution of sodium carbonate. It is not recommended to establish a clearly alkaline reaction before the precipitation of proteins (which occurs during subsequent boiling), as this prevents the clearing of the medium. To the resulting liquid, add the white of a fresh egg stirred in a small amount of distilled water, which subsequently achieves complete transparency of the medium; the mixture is well shaken and boiled in a water bath or Koch apparatus for 1 hour. Next, the reaction is checked again, the medium is alkalized if the reaction turns out to be acidic; in the latter case, the medium is boiled for another 15-20 minutes and filtered through a double filter, previously moistened with hot water. For filtering, it is convenient to use a heating funnel, where the temperature is maintained at about 60°. The finished gelatin is poured into sterile test tubes or flasks and sterilized fractionally for three days in a row for 15-20 minutes at 100°. Gelatin liquefies at 24-32°. Repeated heating and heating to a high temperature have a detrimental effect on the ability of gelatin to solidify. For growing certain microbes and for other special purposes, the composition of nutrient gelatin is modified in a known way: for example, milk or grape sugar is added in an amount of 0.3-0.5% before sterilization, the content of table salt is changed, a solution of iron is added, etc.