465 



PROTEIN. 



PROTEIN. 



Whether Protein can be formed within the animal body is uncertain, 

 but it cannot be doubted that the Protein compounds in vegetables 

 are imparted to animals in their food, and as the compounds form the 

 principal component parts of the animal body, this constituent must 

 be supplied either wholly or in part by plants. 



The Protein compounds existing in plants were till quite recently 

 known as Soluble Albumen, Coagulated Albumen, Legumin, and Gluten; 

 Liebig has however applied to the three first the names Vegetable 

 Albumen, Vegetable Fibrin, and Vegetable Casein, asserting that they 

 are identical in their physical properties and in their chemical com- 

 positions with the corresponding principles in the animal kingdom. 

 Mulder, the discoverer of Protein, denies the accuracy of this state- 

 ment. " The special character of these animal substances is," he 

 remarks, "determined by the small portions of sulphur and phos- 

 phorus they contain, by which they differ from each other and from 

 pure Protein. The proportions of sulphur and phosphorus in the 

 three vegetable substances are still unknown; and therefore the 

 names proposed by Liebig cannot be applied to them. Moreover both 

 vegetable albumen and legumin differ so much from animal fibrin and 

 casein, both in form and appearance, that they ought not to have a 

 similar name." 



Soluble Vegetable Albumen is that substance which, being soluble 

 in water, is precipitated from the juices of plants by heat, alcohol, or 

 acid*. It is soluble in weak alkaline fluids, from which it is precipi- 

 tated liy acids, and, independently of the sulphur and phosphorus, 

 has the same composition as Protein. Coagulated Vegetable Albumen 

 is the compound of protein, sulphur, and phosphorus, which is in- 

 soluble in water ; it exists in the seeds of the Cerealea, in almonds, 

 Ac. Glutin is t'je substance which can be extracted by alcohol from 

 the ordinary gluten by washing away the starch from flour. 



The Protein-compounds contained in the animal body correspond to 

 these in the vegetable. Thus we have Fibrin, Albumen, and Casein. 



The bodies of animals contain Fibrin both in a fluid and a solid 

 state ; in the former it exists in the blood, and in the latter form in 

 muscular fibre, but that of venous differs from that of arterial blood. 

 To obtain the former, human blood ia to be triturated in a mortar 

 with one and a half times its weight of water, and one third of its 

 weight of nitre ; and the mixture is to remain, during at least twenty- 

 f>ur hours, exposed to a temperature of about 100 to 120 Fahr. ; by 

 this it ii rendered slimy and gelatinous, and at length it becomes 

 liquid, exhibiting the properties of albumen which has been treated 

 with acetic acid. When largely diluted with water, a flocculent sub- 

 fiance is thrown down, which closely resembles coagulated albumen. 

 When arterial blood is employed in the same way similar changes are 

 not produced, and the fibrin of venous blood loses the property if it 

 has absorbed oxygen. 



Solid Fibrin is procured by washing thin portions of muscular flesh 

 in cold water until they are rendered quite white, or in a purer state 

 by stirring fresh blood with a stick to which the fibrin adheres : it is to 

 be rendered pure by washing first with cold water, and afterwards by 

 treatment with ether. Fibrin, when fresh, exists in the state of long, 

 white, elastic filaments; it is inodorou?, tasteless, and insoluble in 

 water whether cold or hot, but by long-continued boiling a portion 

 is dissolved. When dried at a gentle heat it loses about four- 

 fifths of its weight, which loss is water, and it becomes then horny 

 and translucent, and very much resembles albumen which has been 

 coagulated ; acetic acid and fresh fibrin when kept for some hours in 

 contact, form a transparent gelatinous mass which is soluble in water; 

 solution of potash dissolves fibrin, and the compound possesses many 

 of the characters which belong to albumen. 

 According to Mulder dried fibrin consists of 



Carbon 54'56 



Hydrogen 6-90 



Azote 1572 



Oxygen 22-13 



Phoaphorus '33 



Sulphur -36 



100 



If it be admitted that the phosphorus and sulphur are hi definite 

 combination, the formula of this substance will be C 1UO H., ln N M , O,.,,, 

 PS, which certainly includes a very unusual amount of equivalents. 

 Its composition is precisely similar to that of coagulated albumen, 

 and, as already remarked, they have several properties in common. 



[FlBKIN.] 



Albumen is found very extensively in the human body, forming the 

 chief ingredient in the serum of the blood, chyle, lymph ; and enters 

 largely into the composition of the brain and nerves. The white of 

 eggs is liquid albumen. It unites with alkalies and metallic oxides, 

 forming albuminates. It is precipitated from its solutions by nitric 

 acid, beat, corrosive sublimate, and metallic oxides generally. The 

 following is its composition : 



From Actual Analysis. Calculated Atoms. 



Carbon . ... 64-38 64-44 C. 48 



Hydrogen .... 7'14 6'99-H. 37 



Nitrogen 15-92 15-88 N. 6 



Oxygen 22-56 22-690. 15 



JUT, HIST. civ. VOL. iv, 



100 



100 



Casein is the basis of the various kinds of cheese, and closely 

 resembles albumen in many properties. It is insoluble in water, but 

 a small portion of alkali renders it soluble ; it may be prepared by 

 adding dilute phosphoric acid to fresh milk warmed ; a coagulum is 

 produced, which after being washed is to be dissolved in a weak 

 solution of carbonate of soda, and this is to be kept in a warm place 

 to allow of the separation of the butter ; these re-solutions in carbon- 

 ate of soda and precipitations are to be repeated several times, and 

 the insoluble casein is then to be washed with boiling water, and 

 treated with ether, to remove any remaining butter or fatty matter. 



Casein thus prepared is a curdy white substance, insoluble in water 

 or alcohol, but soluble by water containing an alkali or its carbonate : 

 dilute acids also dissolve a small portion of it. When moist, it 

 reddens litmus-paper, and leaves about 0'3 per cent, of ashes by in- 

 cineration. Casein is coagulated by certain animal membranes, as 

 is shown in the process of making cheese, in which, by the action 

 of a piece of the stomach of the calf, milk is separated into a 

 yellowish liquid termed whey, and a solid white coagulum which 

 contains all the casein of the milk with portions of some of its other 

 principles. 

 According to the analysis of Mulder, casein consists of 



Carbon 54'98 



Hydrogen 7'15 



Azote 15-80 



Oxygen 21'73 



Sulphur -36 



100 



The following are also formula for these substances: 



Fibrin from blood 10 (C,,, H 3 , N- 0,.,) + SP, or 10 FF+SP; that it 

 to say, every atom or equivalent of fibrin contains 10 atoms or equiva- 

 lents of Protein with one each of sulphur and phosphorus. 



Albumen from the serum of the blood is represented by 10 (C,,, 



3i N s 9i ? ) * S 2 P > or 1 P* + S -J P J tllat "> to sav > il; differs from fibriu 

 ui containing one atom more of sulphur. 



Casein from cow's milk, 10 (C w H 31 N 3 0, a ) + S, or 10 "Pr + S. 

 Ci-yitallin, the substance that forms the principal constituent of the 

 lens, 15 (C M H 3I N 3 12 ) + S, or 15I>r + S. 



These are all the Protein-Compounds of the animal body yet known. 

 The muscular fibre is for the most part composed of a Protein-Com- 

 pound, fibrin, which likewise exists in the circulating Quids ; and 

 albumen occurs in the brain, liver, kidney, and many other organs, us 

 well as in the blood. The above compounds of Protein enter into 

 some very important combinations, a few of which, from their physio- 

 logical bearings, we shall here notice. The combinations of the 

 leading Protein-Compounds, fibrin, albumen, and casein, with alkalies, 

 acid', and salts, are especially remarkable. Protein is soluble in weak 

 alkalies, and according to Mulder it exists in the blood as a proteato 

 of soda with sulphur and phosphorus. Eudeiiin and the Giessen 

 school, oil the other hand, deny that it exists in that fluid as proteate 

 of soda. They assert that the cause of the alkalinity of the blood is 

 the presence of the ordinary tribasic phosphate of soda a salt which 

 has the power of dissolving the Protein-Compounds : the question 

 whether Mulder or Enderlin bo correct is still undecided. 



On neutralising a weak alkaline solution of Protein by an acid, its 

 solubility is greatly diminished ; a fact which Mulder regards as 

 elucidating the medical properties of certain acids. The sulphuric 

 and phosphoric acids, for instance, possess the property of stanching 

 blood; acetic acid, on the contrary, by which Protein is readily dis- 

 solved, is destitute of that property. Very dilute hydrochloric acid 

 occurs in the stomach, and as it possesses the property of dissolving 

 Protein, it doubtless renders the food (at least the portion consisting 

 of Protein-Compounds) tender, and thus assists digestion. Some 

 acids enter into combination with the Protein-Compounds, producing 

 comparatively insoluble bodies. For this reason certain acids 

 (sulphuric and hydrochloric) are very efficacious in putrid fevers, 

 scurvy, &c. As an illustration of the combinations of the Protein- 

 Compounds with salts, we may notice that of bone-earth with casein. 

 Bone-earth is a phosphate of lime whose composition is represented 

 by the formula 3 P., Oj + 8 Ca 0. In casein, and therefore in milk, it 

 exists in great quantity, and this seem 1 ) to supply a large amount of 

 earthy matter to the tender bones of young animal?. 



In addition to albumen and fibrin, a third Protein-Compound exists 

 in the blood, constituting the cell-wall of the corpuscles. It is termed 

 Globulin. Its real composition is unknown; Simon regards it as 

 casein. All these Protein-Compounds contain more or less phosphate 

 of lime, which thus finds its way to the bones. 



Two other very important Protein-Compounds exist in the animal 

 body, namely the binoxide and tritoxide of Protein. They both 

 exist to a large amount in the blood in inflammatory diseases, and to 

 a small amount in healthy blood. The latter is soluble iu water, the 

 former is not. At every respiration a small amount of them is pro- 

 duced in the blood, and Mulder (who must be regarded as the highest 

 authority in all that relates to Protein) believes that they form around 

 the blood-corpuscles a thin layer, having the same composition as the 

 buffy coat or inflammatory crust. Gelatin is a degraded form of 

 Protein. [GELATIN.] 



2s 



