Fibrin

Fibrin, a protein substance obtained from fibrinogen of blood plasma during processes of clotting (see Blood, blood clotting). Pure freshly precipitated F. represents a gelatinous elastic substance, of fibrous appearance under the microscope. Depending on the time of formation and the admixture of various formed elements, the color and consistency of F. change accordingly. Precipitation of F. is observed in the vascular bed, as well as outside vessels—in extravasated blood and in pathological effusions. Under pathological conditions, clotting of fibrinogen takes place in the bloodstream in processes of thrombus formation and in postmortem clotting of blood. In lymphatic vessels, fibrinogen can also clot, especially during resorption of protein-rich pathological effusions. Precipitation of F. is usually observed in extravasated blood, and the rate of clotting depends to a large extent on the site of hemorrhage; thus, in hemorrhage into the abdominal cavity, blood can remain liquid for a comparatively long time due to the endothelium lining the peritoneum. One or another admixture of F. can be observed in exudative inflammations, depending on the amount of protein and the quality of its fractions (see Inflammation). When transudate is supersaturated with protein and cooled (on a corpse, in evacuated ascitic fluid), F. can precipitate in the form of gelatinous clots. The fate of F. varies depending on a number of general and local conditions. F. can undergo autolytic dissolution and be resorbed, can become hyalinized, calcified; often F. is overgrown with connective tissue (organization phenomena), which leads to the formation of adhesions, obliteration of cavities, sclerosis of the organ. A substance morphologically similar to fibrin, so-called fibrinoid, giving the same staining reactions as it, arises in the so-called fibrinoid transformation of connective tissue, observed as a necrotic process in various intoxications and inflammation (rheumatism, dysentery, smallpox, etc.). On sections stained with hematoxylin-eosin, F. is stained by eosin in pink color. By van Gieson-picric acid in yellow color. Of the special methods for detecting F., the most commonly used is Weigert's method, which is a modification of Gram's method, which consists in replacing alcohol with another differentiating fluid (see Gram's method). Instead of carbolic gentiana, it is more convenient to use two basic solutions: 1) absolute alcohol-33 cm³, aniline oil-9 cm³, methyl violet-in excess; 2) saturated aqueous solution of methyl violet; both solutions are mixed before use in the ratio 3:27. Staining: 1) stain sections with just filtered dye for 5-10 min.; 2) wash sections in water and blot them with filter paper; 3) act with Lugol's solution for 15-20 sec. and blot with filter paper; 4) differentiate in a mixture of 2 parts aniline oil and 1 part xylene (under microscopic control); 5) thoroughly wash sections in xylene and mount in Canadian balsam. F. is stained blue, similarly many Gram-positive microorganisms, mucus, and horny substance are stained. Both celloidin and frozen sections can be stained, and mounting on a slide is not necessary. The staining works best on material fixed with formalin. If after fixation with chrome salts the staining does not come out well, it is recommended to place sections for 15-30 min. in 1/8% solution of potassium permanganate, wash with water and transfer for 2-3 hours to 5% solution of oxalic acid, after which again wash with water and then stain. Schueninov's method. Pieces are fixed in any way, preferably with formalin: 1) place sections for 12-24 hours in 3% solution of hydrogen peroxide; 2) stain for 15-20 min. in the following mixture: hematoxylin-1.75, 2.5% aqueous solution of crystalline carbolic acid-200 cm³, 10% aqueous solution of phosphotungstic acid-10 cm³ (the hematoxylin solution should mature in the light for several weeks); 3) wash sections in water and differentiate for 1-12 hours in 5-10% solution of phosphotungstic acid; 4) wash sections with water, dehydrate and mount in Canadian balsam. F. is stained dark blue. Schueninov's method is simpler and has the additional advantage that it stains the entire mass of F., which may not always be the case with Weigert's method. r. Khurgish. Elementary composition of F.: C-52.58%, H-6.83%, N-16.91%, S-1.10%, O-22.48%. F. is a white fibrous elastic substance, which in dry form can be rubbed into powder. In solubility, it stands close to denatured proteins. It does not dissolve in water, alcohol, ether. When heated, it contracts; it swells strongly and at room temperature very slowly (within several days) dissolves in diluted (0.1%) acids and alkalis, being decomposed in the process. It is difficult to dissolve in diluted NaCl solution, easily dissolves at 40° in 6% solution of NaNO₃, however being decomposed in the process. If F. is left standing with the blood in which it was formed, then after some time (Dastre) partial dissolution of F. (fibrinolysis) is observed, which must be taken into account in quantitative determinations of F. Recently, attempts have been made to use fibrinolysis for preparing blood for transfusion. Strong fibrinolysis is observed in the blood in acute phosphorus poisoning (Jacoby), after extirpation of the liver (Noli), after injection of albumoses into the blood. F. obtained from the blood of various animals differs somewhat in properties; thus, for example, F. of pigs is much more easily dissolved in 0.5% HCl than F. of ox. For the isolation of F. and for its quantitative determination, the liquid under examination (to liquids incapable of spontaneous clotting, serum is preliminarily added) is vigorously stirred with a fish bone; the resulting F. clot is washed with water, then with 5% solution of NaCl, again with water and extracted with alcohol and ether. Fibrinogen is contained in blood plasma, lymph, chyle, some transudates and exudates, in bone marrow and possibly in other lymphoid tissues, in leukocytes, in urine in albuminuria, in hydrocele, in the fluid of the pericardial sac of an ox. Absent in blood serum. For the isolation of fibrinogen according to Hammarsten, oxalate plasma is left standing in the cold for the precipitation of a sediment containing prothrombin, which is filtered off; then an equal volume of saturated NaCl solution is added to the plasma; the resulting fibrinogen precipitate is filtered off, pressed out, dissolved in 8% solution of NaCl and again precipitated with saturated NaCl solution; such treatment is repeated 3 more times; the fibrinogen precipitate is dissolved by adding a small amount of water and purified from NaCl by dialysis. For fibrinogen of horse blood [«]d=-52.5°. Fibrinogen precipitated by water or diluted acid soon becomes insoluble. For other properties of fibrinogen—see Blood. The place of formation of fibrinogen was considered to be leukocytes (Mathews), bone marrow (Miiller), spleen, lymphatic glands and other lymphoid organs, liver (Doyon, Nolf and others); recent works speak in favor of the hepatic origin of fibrinogen, if the influence of accelerated fibrinolysis is considered excluded. Thus, extirpation of the liver causes a decrease in the fibrinogen content in the blood; disease of the liver parenchyma leads to a decrease in the fibrinogen content in the blood; in phosphorus poisoning, fibrinogen can completely disappear from the blood; in chloroform poisoning, the fibrinogen content in the blood decreases with liver damage and again increases with its restitution; according to Duyon's research, the blood of hepatic veins is richer in fibrinogen than the blood of other vessels (see also Blood). Processes accompanied by destruction of cells in the body apparently always give an increase in the fibrinogen content in the blood. Methods of quantitative determination of fibrinogen are mostly based on its conversion to fibrin. The minometric method of Fonio is based on the fact that the more fibrinogen, the greater the dilution at which clotting is still observed. In the method of Volgemuth, decreasing amounts of fibrinogen (oxalate plasma) are added to equal amounts of thrombin (fresh serum) and the smallest amount of fibrinogen that still causes the formation of fibrin threads is noted. Refractometric determination of fibrinogen is carried out by the difference in the refraction of serum and plasma. The method of Porges and Spiro is based on determining the difference in nitrogen content in serum and plasma. Fibrin of Henle—a white cottony precipitate obtained by diluting male semen with water. Fibrinous stones, a variety of concretions found in renal calyces. The main mass of these stones is fibrin. In appearance and consistency, F. s. resemble protein and bacterial stones, and therefore for clarification of diagnosis it is necessary to perform staining for fibrin by Weigert's method. F. s. have the consistency of a boiled bean, in size can be up to a plum, usually round in shape. They occur in quantities from one to several tens. On cross-section, fibrinous stones have a layered structure at the periphery and an amorphous center.

When stained by Weigert's method, the layers are well-stained, revealing a delicate fibrous structure; the amorphous center is stained less intensely. Sometimes remnants of erythrocytes and plates are visible in the center. Bacteria can be seen in all layers, and leukocytes are found in the superficial layers. As a rule, F. c. are encrusted with calcium phosphate or urates. - F. c. are quite rare. Their first description in the literature appeared in 1838 (monograph by Marcet). They are observed at all ages - in both 2-week-old newborns and the elderly. The formation of F. c. usually occurs in the presence of chronic purulent inflammation of the kidneys and renal pelvis, or after renal hemorrhages. But despite the fact that these diseases are common, F. c. still form extremely rarely. In recent years, the mechanism of their formation tends to be explained from the standpoint of the Lichtwitz-Schade stone formation theory - the accumulation of colloids in the urine of an inflamed kidney with subsequent deposition of concretions. During life, the stones are diagnosed radiologically, but of course as ordinary kidney stones.