The filtrate contains the

ALBUMINS

Dialyse away excess of salt. Saturate with ammonium sulphate; wash the precipitated albumins with saturated solution of ammonium sulphate; dissolve the precipitate by adding water; excess of salt may again be removed, if necessary, by dialysis. A solution of pure albumin is thus obtained. Add ether, egg-albumin is precipitated, serum-albumin remains in solution.

VITELLIN (a globulin), which is very imperfectly precipitated by salt, may be mixed with the albumins. If so, it will be precipitated by dialysis. (For crystalline vitellin see p. 133.)

c. Slightly acidify the solution and boil; the albumin and globulin are coagulated; filter off the precipitate, and again test for acidalbumin and alkali-albumin. See a.

TABLE III. To separate the coagulable proteids (albumins and globulins) from the non-coagulable (albumoses and peptones)

a. Saturate with ammonium sulphate. All proteids are precipitated but peptones; filter off the precipitate; the peptones are in the filtrate.

b. Boil (after acidification). This precipitates the albumins and globulins; filter. The filtrate contains the albumoses and peptones, which may be separated as in Table IV. This method is only applicable to concentrated solutions, as small quantities of primary albumoses are apt to be formed by the hydrating action of the acidified hot water from the albumins and globulins.

c. Add ten times its volume of alcohol to the solution. This precipitates all the proteids. Leave the precipitate under absolute alcohol for at least one-better two or three months. Pour off supernatant alcohol, evaporate the rest of the alcohol at 40° C. Add water. The albumoses (except dys-albumose) and peptones enter into solution. Separate as in Table IV. Albumins and globulins are, as a result of the prolonged action of alcohol, insoluble in water or saline solutions. d. Saturate with magnesium sulphate. A precipitate is produced; filter this off.

The precipitate contains globulins, proto-albumose, and heteroalbumose. Separate these as in

b or c.

The filtrate contains albumin, vitellin, deutero-albumose, and peptone. Separate as in b and c. For the separation of vitellin, precipitate it by dialysis as in Table II.

TABLE IV. Separation of proteids when more than one is in solution; globulins, albumins, and albuminates being absent.

The solution will contain proteoses (albumoses) and peptones. Faintly acidify with acetic acid, and fully saturate with ammonium sulphate. A precipitate is produced, filter this off.

The precipitate consists of

ALBUMOSES

Wash the precipitate with saturated solution of Am2SO4. Redissolve the precipitate | by adding water. Render the solution faintly acid with acetic acid. Saturate with sodium chloride, and filter off the precipitate.

the

The filtrate contains

PEPTONES

To separate these in a pure state, evaporate the solution to a small bulk, filter off the crys tals of ammonium sulphate which separate, and the remainder of the salt by aqueous baryta, and the last traces by barium carbonate. Precipitate the excess of baryta by dilute sulphuric acid; filter off the barium sulphate thus precipitated. To the filtrate add excess of alcohol; this precipitates the peptones; redissolve them in a small quantity of water, and reprecipitate by phos| pho-tungstic acid; wash the precipitate with alcohol and ether, and dry.

CHAPTER XI

THE ALBUMINOIDS, FERMENTS, AND PIGMENTS

THE ALBUMINOIDS

THE term albuminoid is used by some chemists synonymously with proteid. It is however best to restrict the name to a group of substances which, although similar to the proteids in many particulars, differ from them in certain other points. No doubt in most cases they originate from proteids. They are especially abundant in the connective tissues and in epithelium, and they will be fully described in connection with these tissues.

1. Collagen. The substance of which the white fibres of connective tissue are composed. It is probably the anhydride of gelatin. 2. Ossein. The collagen from bone.

3. Gelatin. The substance produced by boiling collagen with water. Soluble in hot, insoluble in cold water. It is not precipitated by acetic acid and ferrocyanide of potassium. It contains no sulphur. (a)=-130°.

By hydrating agents, such as heating with superheated steam, treatment with gastric juice, &c., it is converted into peptone-like substances, intermediate bodies analogous to the proteoses being formed. Salkowski' gives the following differences between proteid-peptone, gelatin, and gelatin-peptone.

4. Chondrigen. The organic basis of hyaline cartilage; it is a mixture of collagen and mucinoid substances.

1 Berlin. klin. Woch. 1885, No. 2.

reddish pp. colourless

colourless

lemon-yellow lemon-yellow

5. Chondrin.--The substance obtainable from chondrigen by boiling. It is a mixture of gelatin and mucinoid substances.

6. Mucin.-A widely distributed substance occurring in epithelial structures (mucus, mucous glands, goblet cells, cement-substance of epithelium), in connective tissues (chief constituent of the groundsubstance); it forms the chief constituent of the bodies of certain invertebrates like the snail; it is found in electrical organs, in synovia, in certain forms of saliva, and in bile. The greater part of the slimy substance in bile is however a nucleo-albumin.

The mucin obtainable from different sources varies in composition and reactions. There are probably several mucins. They all agree in the following points.

(a) Physical character. Viscid, slimy, tenacious.

(b) Precipitability from solutions by acetic acid; they are insoluble in excess of this reagent. They all dissolve in dilute alkalis.

(c) They are all glucosides: compounds of a proteid (probably variable, but generally a globulin) with animal gum, which by treatment with dilute sulphuric acid can be hydrated into a reducing, but non-fermentable sugar.

7. Colloid-substance.-This occurs in the thyroid gland, and in certain forms of tumour, especially those connected with the thyroid (goître) or with the ovary (see ovarian cysts). Acetic acid causes it to swell, but does not precipitate it, otherwise it resembles mucin.

8. Met-albumin or pseudo-mucin is the same as colloid substance (see ovarian fluid).

9. Paralbumin is met-albumin in loose combination with proteid substance.

10. Lardacein.-This substance occurs in that form of degeneration called waxy or albuminoid degeneration. It specially affects small blood vessels, but it may also involve the tissue-elements of organs like the liver, spleen, pancreas, &c. This form of degeneration occurs especially in cases of chronic pus-formation. The parts affected become brownish-red, as glycogen does on the addition of iodine, and bluish or violet on the addition of sulphuric acid and iodine. It was therefore supposed at one time to be of the nature of a carbohydrate, and was called amyloid substance by Virchow. Kekule has, however, shown i that it is nitrogenous, and is probably an intermediate step between albuminous matter on the one hand and fat and cholesterin on the other. It is insoluble in water, alcohol and ether. Dilute acetic acid has no effect on it, except that the strong acid causes it to swell. It is insoluble

1 Kekule and Friedreich, Virchow's Archiv, xvi. 58. See also Kühne, Maly's

Jahresb. iii. 31.

in alkaline carbonates, but dissolves in strong alkalis. Until quite recently it was also stated to be insoluble in gastric juice; but although it is acted upon with difficulty, gastric juice does ultimately dissolve it (Kostiurina).1

11. Elastin. This is the substance of which the yellow fibres of connective tissue are composed. It is a very insoluble material. The sarcolemma of muscular fibres and certain basement membranes are very similar.2

On digestion, elastoses (substances analogous to the proteoses) are formed.3

12. Nuclein.-The chief constituent of cell-nuclei.

A similar substance is also found in milk, and yolk of egg. Its physical characters are somewhat like mucin; it however contains abundance of phosphorus.

A substance very similar to nuclein has been made artificially by adding metaphosphoric acid to albumin. Nuclein and the chromatin of histologists are probably identical. (See The Nucleus, Chap. XIV). 13. Plastin. Another highly phosphorised substance found in nuclei and cell-protoplasm.

14. Nucleo-albumins.-Compounds of proteids (generally globulins) with nuclein.

These are constituents of cell protoplasm, and are perhaps identical with the plastin of microscopists. The mucin-like substance in bile is a nucleo-albumin.

15. Spermatin is the mucin-like substance in semen. It however differs from mucin in being soluble in excess of acetic acid. Possibly it also may be a nucleo-albumin.

16. Hyalins and Hyalogens.—A group of substances very like the mucins, chiefly found in invertebrate connective tissues (Krukenberg. See Chapter XXII).

17. Keratin.-Horny material. See Chapter XXI.

18. Eleidin.-A stage in the formation of keratin.

19. Skeletins.-A name given by Krukenberg to a number of insoluble epithelial products found chiefly in invertebrates. The group includes chitin, conchiolin, cornein, spongin, fibroin, and silk (See Chapter XXI).

1 Chem. Centralbl. 1887, p. 120.

2 Certain minor differences have been recently pointed out by Ewald, Zeit. Biol. xxvi. 1.

3 Horbaczewski, Zeit. physiol. Chem. vi. 330. Chittenden and Hart, Zeit. Biol.

XXV. 368.

L