By artificial gastric digestion the bands are altered, and this constitutes what MacMunn calls modified myohæmatin. Modified myohæmatin can be obtained in solution by covering the blood-free muscles

FIG. 70.-1, Absorption spectrum of myohæmatin. First band, A 613-600; second band, à 569563; third band, A 556 550, this is the best marked band: fourth band, an ill-defined shading over the line. 2, Absorption spectrum of modified myohæinatin. First band, à 554-5-548-5: second band, à 524-5-519.

with ether for some days. A yellow lipochrome derived from the fat between the muscular fibres passes into solution, and below this floats a red juice which shows the two bands of modified myohæmatin (fig. 70, spectrum 2); these resemble those of hæmochromogen, but are placed rather nearer the violet.

The Extractives of Muscle

The method of preparation and chief properties of each of these substances will now be taken

up seriatim.

Creatine. If an aqueous infusion of meat be made, and the proteids

1 Halliburton, Journ. of Physiol. vii. 325.

precipitated by boiling and filtering off the coagulum so formed, the extractives and salts remain in solution. Beef tea is a liquid which contains little more than extractives and salts; Liebig's and other commercial meat extracts are virtually the solid residues obtained on evaporating aqueous infusions (from which the proteids have been separated) to dryness.

The following methods of preparation may be adopted :

1. To an aqueous extract of meat (minus its proteids) add baryta to precipitate the phosphates; filter; remove excess of baryta from the filtrate by a stream of carbonic acid; filter off the barium carbonate ; and evaporate the filtrate on the water-bath to the consistency of a thick syrup. Set it aside to cool, and in a few days crystalline deposits of creatine will be found at the bottom of the vessel. These are washed with alcohol and dissolved in hot water. On concentrating the aqueous solution crystals once more separate out, which may be still further purified by recrystallisation (Liebig).

2. The aqueous extract is precipitated with acetate of lead; filtered; the filtrate freed from excess of lead by a stream of sulphuretted hydrogen, and then filtered and evaporated till crystals appear, which may be purified by recrystallisation (Neubauer 2). Städeler3 uses an alcoholic instead of an aqueous extract of muscle.

3. Muscle is finely chopped and allowed to stand under ether; a strongly acid, watery fluid in a day or two separates out; this is red owing to the presence of myohæmatin; the ether floats above this watery liquid. On evaporating the latter, crystals of creatine separate out, and may be purified by recrystallisation as before (MacMunn1).

Creatine has the formula C,H,N30,; this unites with one molecule of water of crystallisation to form transparent, colourless, monoclinic prisms (fig. 34, p. 84). The crystals lose their water of crystallisation at 100° C. They are soluble in water, especially in hot water, and almost insoluble in absolute alcohol and in ether, sparingly soluble in rectified spirit.

Creatine forms crystalline compounds with the mineral acids, and with mercury (C,H,HgN ̧O2).

When creatine is treated with various reagents it undergoes a number of different decompositions. The most important of these are the two following, as it is probable that similar changes occur in the body:

(a) Conversion into creatinine. When creatine is heated with dilute

1 Ann. d. Chem. u. Pharm. Ixii, 257.

J. f. prak. Chem. lxxii. 256.

2 Ibid. exix. 27.
Journ. of Physiol. viii. 58.

mineral acids, or for several days with water, it loses a molecule of water, and creatinine is formed :

A similar change occurring in the body no doubt gives rise to the creatinine occurring in the urine.

(b) Conversion into sarcosine and urea.-Creatine seems to replace urea in muscular tissue; the theory that it is a stage in the formation of urea has been advanced because it can be made to yield urea in the laboratory; its molecule, in fact, contains the cyanamide radicle (CN.NH2), which plus a molecule of water is equal to urea (CONH1). (See further under Urine.)

When creatine is boiled with baryta water, the following equation represents the change that occurs :—

C1H2N3O2+H2O=CON2H1+C2H,NO2

4

[sarcosine]

Synthesis of creatine.—Creatine has been made synthetically, and the following, which is the method adopted, will show what is the constitution of its molecule.

When methylamine and monochloracetic acid are brought together, the following reaction occurs :-

That is to say, sarcosine and hydrochloric acid are formed.

Sarcosine

is also called methylglycocine, i.e. glycocine (amido-acetic acid), in which one H is replaced by methyl (CH3). On heating sarcosine and cyanamide together, creatine is formed according to the following equation:

Quantity of creatine in muscles.-According to Voit the quantity of creatine is fairly constant in the voluntary muscles; the quantity is found to vary from 0-2 to 0·3 per cent. in different animals. This quantity increases during starvation (Demant 4). Cardiac muscle

1 Creatine is also found sparingly in nervous tissue.

Creatine is thus methyl-guanidine-acetic acid (Baumann, Ann. Chem. Pharm. clxvii. 77).

Zeit. f. Biologie, iv. 77. Subsequent analyses by Neubacter, Hofmann, Creite, and many others have confirmed Voit's analyses. For references see Hoppe-Seyler's Physiol. Chem. p. 642. 4 Zeit. physiol. Chem. iii. 387.

contains less creatine than the voluntary muscles (Voit); the same is true for unstriated muscle (Lehmann 1).

7

2

Creatinine. Small quantities of this base are found in muscle; it is also a constituent of urine. The strongly alkaline reaction of creatinine is said by Salkowski in a recent article 3 to be greatly due to adherent alkaline salts. The compound of creatinine with zinc chloride (C,H,N ̧O)¿ZnCl, has a characteristic crystalline form, and is used as a test for this substance. The statements made as to the relative quantities of creatine and creatinine during the rest and activity of muscle are contradictory; Voit states that creatine is diminished during activity; Sarokin' that creatinine increases during tetanus; and Nawrocki contradicts these statements. The more recent observations by Monari however confirm the original statement of Sarokin; on fatigue of muscle, creatinine is produced from the creatine, together with a small quantity of another substance called xanthocreatinine CH1NO.

Hypoxanthine, Xanthine, and Uric Acid are found in muscles in small quantities.

The formula of these three substances denote their close relationship to one another.

The last-mentioned substance, uric acid, occurs only in the merest traces (Meissner). With regard to xanthine" and hypoxanthine," the following is a summary of the chief facts concerning them :

Preparation. The mother liquor, from which creatine has been separated, is precipitated with ammonia and silver nitrate; the precipitate is dissolved in nitric acid of specific gravity 11. The liquid is cooled and a compound of hypoxanthine and silver nitrate crystallises out. The mother liquor (a) is preserved. The silver is removed from the crystals by sulphuretted hydrogen, and the nitrate of hypoxanthine treated with ammonia, and thus crystalline nodules of hypoxanthine are formed. A compound of xanthine and silver nitrate is left in solution in (a); it is precipitated by excess of ammonia; the silver is removed by sulphuretted hydrogen, and the base obtained in white amorphous granules by adding ammonia.

1 Lehrbuch, iii. 73.

This is, however, denied by Neubauer and Nawrocki.

3 Salkowski, Zeit. physiol. Chem. xii. 211.

5 Virchow's Archiv, xxvii.

7 A. Monari, Gazetta, xvii. 367.

? Found also in urinary calculi (Marcet), in guano

4 Loc. cit.

6 Centralblatt, 1865, p. 417. 8 Zeit. f. rat. Med. xxxi. 144. (Unger and Phipson, Chem. Med.

vi. 16), and in urine (Bence Jones, Quart. J. Chem. Science, xv. 78; Weiske, Zeit. f. Biol.

ii. 254).

10 Found also in spleen (Scherer), in the blood, marrow, and secreting glands.

Xanthine

Properties. It reduces silver salts. It forms compounds with hydrochloric acid (hexagonal plates), nitric acid, &c. ; the latter is not rendered purple by ammonia, and so it can be distinguished from uric acid.

Amount in muscle.--0.0026 (Scherer').

Hypoxanthine

It forms compounds with silver, copper, and platinum. On oxidation with nitric acid it yields xanthine. Its nitrate and chlorate are crystalline.

0.022-0.026 (Neubauer 2). Its amount increases in starvation (Demant).

Carmine. A crystalline base (C,H,N,O,+H,O); it was originally found in fairly large quantities (1 per cent.) in American meat extracts (Weidel3); it has been since found in the flesh of several animals (frog, alligator, &c.) by Krukenberg and Wagner. It is probable that carnine is one of the intermediate products between the proteid molecule and the substances of the uric acid group which we have just considered.

4

Urea. (CON,H,) is probably present in small quantities, but is difficult to separate from other nitrogenous bases.

Taurine.-Found in the muscles of the horse, fishes, and molluscs. In fishes Limpricht found 1:06 per cent. of taurin.

5

Glycocine. Found to the extent of 0.39-0-71 per cent. in the non-striated muscles of molluscs (Chittenden ").

Protic acid (Protsäure).—An acid formed from the decomposition of proteids, described by Limpricht in the muscles of fishes. This is an acid of doubtful

nature.

Inosinic acid (C1H,,N,O).-First described by Liebig. It is itself amorphous, but forms crystalline salts with the alkaline metals, with barium, and with calcium. It has since been found and estimated (0.005-0.02 per cent.) by Creite.

Lecithin and its decomposition products, such as glycerophosphoric acid, are found in small quantities in muscle, but it is very doubtful whether this substance is a constituent of muscular substance proper; more probably it is derived from the nerve fibres which terminate in the muscle (Hoppe Seyler $).

The next class of extractives are those which are non-nitrogenous; these are glycogen, inosite and other carbohydrates, lactic acid, and fat.

Glycoger. This substance, sometimes called animal starch, has the formula (C6H1005). It is present largely in all embryonic tissues;"

1 Ann. Chem. Pharm. cvii. 314.

3 Weidel, Ann. Chem. Pharm. clviii. 353.

2 Zeit. f. anal. Chem. vi. 33.

4 Krukenberg and Wagner, Sitzungsber. d. physik.-med. Gesell, zu Würzburg, 1883, No. 4. Krukenberg has also examined the muscles of a large number of fishes and invertebrates for the presence or absence of the various extractives enumerated above. His results will be found in Untersuch. des physiol. Anstalt Heidelberg, vol. iv. Heft i.; and in Maly's Jahresbericht, x1. 340.

Ann. Chem. Pharm. cxxvii. 185, cxxxiii. 300.

6 Ibid. clxxviii. 266.

8 Physiol. Chem. p. 647.

7 Zeit. rat. Med. (3) xxxvi. 195.

9 Claude Bernard, Comptes rend. xlviii. 673. Cramer (Zeit. Biol. xxiv. 67) obtained pure glycogen from foetal skin and cartilage.