378 ALBUMINOIDS. 



It is also readily thrown down by saturation with sodium chloride, and gives a faint biuret- 

 lvaction (Martin).] 



[Vegetable Casein is said to occur in the seeds of leguminosae ; and it is slightly soluble in 

 water, but readily so in weak alkalies and in solutions of basic calcic phosphate. A solution of 

 this body js precipitated by acids and rennet. Two varieties have been described, (o) legumin, 

 in peas, beans, lentils ; acid in reaction, soluble in weak alkalies and very dilute HC1 or acetic 

 acid ; (/B) conglutin, a very similar body occurring in hops and almonds. The existence of 

 vegetable casein is denied. Vines states that both legumin and conglutin are artificial products, 

 being formed from the globulins present by the dilute alkali used in extraction of the proteids. 

 This is denied by Ritthausen.] 



[Gluten and Glutin. Gluten is readily prepared from flour by washing and kneading it in a 

 muslin bag under a stream of water. So prepared it is yellowish-brown in colour, very sticky, 

 and capable of being drawn out into long shreds. It is insoluble in water, soluble (but not 

 completely) by prolonged action in dilute acids and alkalies ('2 per cent. KHO and HC1). The 

 prolonged action of alcohol (80 to 85 per cent.) dissolves part of the substance of gluten, leaving 

 a residue, called by Liebig plant-fibrin and by Ritthausen gluten-casein. The alcohol contains 

 gliadin (glutin), gluten-fibrin, and mucedin. Gluten-casein is readily soluble in dilute alkalies, 

 almost insoluble in dilute acetic acid, and quite insoluble in cold and boiling water ; the pro- 

 ducts of its decomposition, by heating with H 2 S0 2 , are leucin, tyrosin, glutamic, and aspara- 

 ginic acids. The three bodies dissolved from glutin by alcohol differ chiefly in their solubility 

 in alcohol and water. Gluten-fibrin, the least soluble, is coagulated by the action of absolute 

 alcohol ; it is readily soluble in dilute acids and alkalies, being precipitated by neutralisation. 

 Gliadin (glutin, plant-gelatin) may be prepared by boiling gluten with water : it deposits on 

 cooling the solution. Though soluble in water at 100 C. at first, it becomes insoluble by the 

 prolonged action of water at that temperature. It is, like gluten -fibrin, soluble in dilute acids 

 and alkalies. Mucedin differs from gliadin in being less soluble in strong alcohol. The water 

 used in washing the flour in the preparation of gluten contains hemi-albumose ( Vines) and a 

 globulin ( Wcyl). Rye-flour, as well as wheaten, yields gluten under similar treatment with water. } 



[Nitrogenous Crystalline Principles. Leucin, tyrosin, asparagin, and glutamic acid have 

 been found in the seeds of plants. ] 



250. (2) THE ALBUMINOIDS. These substances closely resemble true proteids in their 

 composition and origin, and are amorphous non-crystalline colloids ; some of them do not con- 

 tain S, but the most of them have not been prepared free from ash. Their reactions and de- 

 composition-products closely resemble those of the proteids ; some of them produce, in addition 

 to leucin and tyrosin, glycin and alanin (amido-propionic acid). They occur as organised con- 

 stituents of the tissues and also in fluid form. It is unknown whether they are formed by 

 oxidation from proteid bodies or by synthesis. 



1. Mucin is the characteristic substance present in mucus. That obtained from the sub- 

 maxillary gland contains C 52*31, H 7 "22, N 11 '84, 28'63. According to Hammarsten it 

 contains S 179 and N 13 "5 per cent. It dissolves in water, making it sticky or slimy, and can 

 be filtered. It is precipitated by acetic acid and alcohol ; and the alcohol precipitate is again 

 soluble in water. It is not precipitated by acetic acid and ferrocyanide of potassium, but HNO3. 

 and other mineral acids precipitate it. It occurs in saliva ( 146), in bile, in mucous glands, 

 secretions of mucous membranes, in mucous tissue, in synovia, and in tendons. Pathologically 

 it occurs not un frequently in cysts ; in the animal kingdom, especially in snails and in the 

 skin of holothurians. It yields leucin and 7 per cent, of tyrosin when it is decomposed by 

 prolonged boiling with sulphuric acid. [The precipitate called mucin has not always the 

 same characters, and, in fact, it differs according to the animal from which it is obtained 

 (Landwehr).] 



2. Nuclein (Micsclwr, 198) (C 29, H 49, N 9, P 3, 22) contains phosphoric acid, and 

 is slightly soluble in water, easily in ammonia, alkaline carbonates, strong HN0 3 ; it gives the 

 biuret-reaction ; no reaction with Millon's reagent ; when decomposed it yields phosphorus. 

 It occurs in the nuclei of pus and blood-corpuscles ( 22), in spermatozoids, yelk-spheres, liver, 

 "brain, and milk, yeast, fungi, and many seeds. It has resemblances to mucin, and is perhaps 

 an intermediate product between albumin and lecithin (Hoppe-Seyler). It is prepared by the 

 artificial digestion of pus, when it remains as an indigestible residue ; acids precipitate it from 

 an alkaline solution. It gives a feeble xantho-proteic reaction ; after the prolonged action of 

 alkalies and acid, substances similar to albumin and syntonin are formed. Hypoxanthin and 

 guanin have been obtained as decomposition-products from it (Kosscl). 



3. Keratin occcurs in all horny and epidermic tissues (epidermic scales, hairs, nails, feathers) 

 C 50-3-52-5, H 6 '4-7, N 16 2-17, O 20'8-25, S 07-5 per cent is soluble in boiling caustic 

 alkalies, but swells up in cold concentrated acetic acid. When decomposed by H 2 S0 4 it yields 

 10 per cent, leucin and 3 '6 per cent, tyrosin. Neuro-keratin ( 321). 



4. Fibroin is soluble in strong alkalies and mineral acids, in ammonio-sulphate of copper ; 

 when boiled with H 2 S0 4 it yields 5 per cent, tyrosin, leucin, and glycin. It is the chief con- 

 stituent of the cocoons of insects and threads of spiders. 



