166 



PROTEIN. 



and membrane. It may be obtained in a state 

 of purity from the blood, in which, as already 

 mentioned, it exists in a soluble condition, but 

 remarkably prone to assume the solid form as 

 soon as removed from the body. The blood, as 

 soon as drawn, should be rapidly beaten up 

 with a bundle of wires or twigs, to which the 

 fibrin attaches itself in the form of solid amor- 

 phous filaments, coloured red by a quantity of 

 the globules entangled in its pores during the 

 coagulation ; these latter may be removed by 

 placing the coagulum in a piece of linen cloth, 

 and washing with a stream of cold water until 

 all colour disappears. It still contains fatty 

 matters, inorganic salts, and a considerable 

 quantity of water, all which may be removed 

 by drying on a chloride of calcium bath at a 

 temperature of about 250, pounding the hard 

 mass in a mortar, washing with alcohol, ether, 

 and dilute hydrochloric acid, and lastly, mace- 

 rating in water until all soluble matter is dis- 

 solved out, when it should be again thoroughly 

 dried. Thus prepared, it is of a yellowish 

 colour, hard, brittle, and, when perfectly free 

 from fat, transparent. It is tasteless, and inso- 

 luble in alcohol, ether, and water ; but in the 

 latter it softens, swells up, and reassumes the 

 appearance it had previous to desiccation. 

 Though insoluble in both hot and cold water, 

 it is converted by prolonged boiling, first 

 into binoxide and eventually into tritoxide 

 of protein, which latter is soluble in water. 

 Most of the acids, when in a concentrated state, 

 cause fibrin to swell up and assume a gela- 

 tinous appearance. It was observed by Scherer 

 that when moist fibrin is placed in an atmo- 

 sphere of oxygen, it has the property of ab- 

 sorbing and retaining a portion of the gas ; an 

 effect no doubt accompanied by the formation 

 of one or more of the oxides of protein : it is 

 probable that a portion of the fibrin of the 

 blood undergoes a similar change, since these 

 oxides are always present in arterial blood both 

 in health and disease, especially in some forms 

 of fever, when, by an accelerated respiration, a 

 larger amount of oxygen is introduced into 

 the system. 



Fibrin and sulphuric acid. With strong sul- 

 phuric acid dry fibrin becomes yellowish and 

 gelatinous, considerable heat being at the same 

 time evolved, sufficient indeed, provided the 

 quantity be large, to cause complete decompo- 

 sition, when it blackens, and sulphurous acid is 

 given off. When water is added, the gelatinous 

 mass contracts suddenly in bulk, and the white 

 curdy matter thus obtained consists chiefly of 

 sulphoproteic acid, already described. 



Fibrin and nitric acid. Fibrin behaves 

 with nitric acid in a similar manner to protein, 

 giving rise to the formation of xanthoproteic 

 acid. 



Fibrin and acetic acid. When treated with 

 concentrated acetic acid, it almost immediately 

 becomes gelatinous, and if water be added and 

 the mixture warmed, it readily dissolves, espe- 

 cially if the fibrin be obtained from a young 

 animal : this solution when evaporated leaves 

 the fibrin with precisely the same properties 

 which it had previous to dissolution. If an- 



other acid, as the sulphuric, be added to the 

 acetic solution, it combines with the protein, 

 forming generally an insoluble compound, as 

 in the case of the sulphobiproteic acid. If the 

 acetic acid solution be neutralized with potash, 

 the fibrin is precipitated, but is redissolved if 

 the alkali be added in excess. 



Fibrin and hydrochloric acid. When treat- 

 ed with strong hydrochloric acid fibrin be- 

 comes gelatinous, and gradually dissolves, giving 

 the solution a beautiful blue colour, which is 

 characteristic of all the protein compounds : if- 

 this solution be diluted with water, a white 

 precipitate appears, which is a compound of 

 hydrochloric acid and protein. When the acid 

 is very dilute it has the property of gradually 

 dissolving fibrin ; and as a trace of free hydro- 

 chloric acid is generally to be found in the 

 stomach, it is probable that its solvent action 

 tends to assist materially in the process of 

 digestion. Bouchardat says that water con- 

 taining only one two-thousandth of its weight 

 of hydrochloric acid causes moist fibrin to 

 become gelatinous, and eventually to dissolve, 

 leaving only a small quantity of insoluble mat- 

 ter, which he calls epidermose: the soluble 

 portion he has called albuminose, but Mulder 

 considers it binoxide of protein, which asser- 

 tion, however, has recently been contradicted 

 by Liebig. 



Fibrin and potash. Fibrin dissolves rea- 

 dily in a solution of potash, even when very 

 dilute. If the solution be gently heated, the 

 fibrin is gradually decomposed, the sulphur 

 and phosphorus being removed, and protein 

 remains combined with the potash, from which 

 it may be separated by neutralizing with acetic 

 acid. Ammonia behaves in a similar manner, 

 but its action is much less rapid. 



Fibrin readily dissolves in the gastric juice, 

 which appears to owe its solvent action both 

 to the organic principle pepsine, and also to a 

 little free hydrochloric acid in the stomach, 

 which is derived from common salt. The same 

 effect may be produced artificially by an infu- 

 sion of the fourth stomach of the calf, to which 

 a little hydrochloric acid has been added. 



It is curious that the presence of certain 

 salts, as nitrate of potash and sulphate of soda, 

 prevents the coagulation of the fibrin of the 

 blood ; and even when coagulated, provided it 

 be still moist, it is again dissolved by some 

 saline solutions, as, for instance, muriate of 

 ammonia. Moreover, M. Denis has found that 

 if moist fibrin be digested in a solution of 

 nitrate of potash containing a little soda, at a 

 temperature of about 100, it becomes gradu- 

 ally converted into a substance in almost every 

 respect identical with albumen, being soluble 

 in water, and coagulable by heat. This change 

 is most readily produced when the fibrin em- 

 ployed has been obtained from venous blood, 

 by allowing it to coagulate spontaneously ; 

 while if it be separated by agitation, or if the 

 blood be arterial, it scarcely experiences any 

 alteration in the saline solution. Changes of 

 this kind, of the several modifications of pro- 

 tein into one another, are constantly occurring 

 in the animal economy, and the great similarity 



