in the adult it is found chiefly in the liver, the muscles, and the white blood corpuscles. During life, as in the liver, the muscle glycogen appears to be converted into sugar, and this change may occur for a certain time after death. Böhm considers the change into sugar does not occur till putrefaction sets in, and Demant 2 has shown that the change may be greatly hindered by the action of weak carbolic acid In estimating the amount of glycogen in muscle, the tissue should, however, be obtained as soon as possible after death, and immediately plunged into boiling water to destroy any ferment which converts glycogen into sugar. The glycogen may then be extracted with hot water (Brücke,3 Nasse 1), or with dilute potash (Abeles, Külz 6). If a quantitative analysis is to be made, a weighed quantity of muscle must be taken, finely divided, and repeatedly extracted until no more glycogen passes into solution. In the case of muscle especially, the dilute alkali effects a much more thorough extraction than hot water (Külz). proteid that passes into solution is precipitated by potassio-mercuric iodide and filtered off; the filtrate is evaporated to a small bulk and the glycogen precipitated as a white powder by excess of alcohol, or it may be converted into sugar and then estimated polarimetrically. Glycogen forms an opalescent solution in water, and gives, like dextrin, a redbrown colour with iodine. A large number of comparative estimations by weighing and by the polarimeter have been made in Külz's laboratory and found to yield very nearly equal results. Cramer," using Külz's method, found

1. The glycogen in the two halves of the body is equal.

Any

2. In the heart, glycogen is unequally distributed in the different regions, so differing from the liver.

3. Different groups of muscles vary in the amount of glycogen they contain, but symmetrical or corresponding muscles contain the

same amount.

Brücke found glycogen in the plain muscle of the stomach; Chittenden 10 and Bizio" found it in the plain muscles of gastropods. The amount of glycogen in muscle is variable; the following are the chief facts relating to variations in the amount that is present :— 1. Influence of starvation. The muscle glycogen in warm-blooded animals

1 Pflüger's Archiv, xxiv. 33.

2 Zeit. physiol. Chem, iii. 200.

5 Brücke, Sitzungsber. d. k. k. Akad. d. Wissensch. Wien, lxiii. 214.

4 Nasse, Pflüger's Archiv, ii. 97.

6 Külz, Zeit. Biol. xxii. 161.

7 Schmelz, Zeit. Biol. xxv. 180.

Abeles, Med. Jahrbücher, 1877, p. 551.

8 Ibid. xxiv. 67.

9 Wiener Akad. Sitzungsber. vol. Ixiii. 2 Abth. 1871.

10 Chittenden, Ann. Chem. Pharm, elxxviii, 266.

11 Bizio, Atti dell' Istituto Venet. di scienze, vol. xi. (ser. 3), 1866.

disappears during inanition much more slowly than the liver glycogen (Weiss,' Aldehoff 2). Luchsinger stated that the heart-muscles are richer in glycogen during inanition than those of the limbs, but Aldehoff, who used Külz's method of estimating glycogen, and therefore obtained more correct results, was not able to confirm this statement of Luchsinger.

2. Influence of work. Muscular activity lessens the amount of glycogen in a muscle, it being apparently transformed into sugar (Weiss, Manché,' Molinari 3). This is well illustrated by the following table (Manché).

In other words, the limbs which were stimulated to contract lost from 12 to 15 per cent, of their glycogen in an hour. Luchsinger considered that glycogen is not a direct source of energy in contracting muscle, but this is in no way proved by his researches, for it is doubtful whether he could ever have obtained muscles free from glycogen-as we have already seen the glycogen of muscle disappears very slowly during inanition. In frogs inanition causes a rapid disappearance of the liver glycogen, but that of the muscles remains practically unaltered (Aldehoff).

3. Effect of removing the liver. Minkowski and Laves stated that after extirpation of the liver the muscle-glycogen markedly diminishes; they consider that the muscle-glycogen chiefly originates in the liver. C. Schmelz, using Külz's method of estimating glycogen, confirms these results which were arrived at by Brücke's apparently less exact method. Schmelz, however, does not consider the point proved that the liver is the source of the muscle-glycogen, for he finds that feeding animals on cane sugar produces no marked increase of the muscleglycogen either in normal animals or in those from which the liver has been removed. Prausnitz also considers that the muscles have a glycogenic function quite apart from that of the liver.

9

No doubt the intact muscles of the healthy limb continue to contract after the operation, and thus lose a certain amount of glycogen; in the paralysed muscles on the other hand, the glycogen is allowed to accumulate.

1 Weiss, Sitzungsb. d. k. Akad. der Wissensch. lxiv.

2 Aldehoff, Zeit. Biol. xxv. 137.

4 Manché, Zeit. Biol. xxv. 163.

3 Luchsinger, Dissert. Zürich, 1875.

5 Molinari, Chem. Centralbl. 1889, ii. p. 372.

Minkowski, Arch. f. exp. Path. u. Pharmakol. xxiii. 139.

7 Laves, Inaug. Dissert. Königsberg, 1886.

8 C Schmelz, Zeit. Biol. xxv. 180.
10 Chandelon, Pflüger's Archiv, xiii. 626.

9 Zeit. Biol. xxvi. 377.

5. Effect of cutting the tendon of a muscle. After tenotomy the muscle appears to be in such a pathological condition that glycogen accumulates in it, and does not undergo metabolic changes so readily as in normal muscle (E. Krauss).1

6. Ligature of the artery supplying a muscle leads to a decrease of its glycogen, especially in those cases in which oedema follows the operation; the saturation of the tissues by lymph leading probably to saccharification (Chandelon, Manché).

Dextrin. This is an intermediate stage in the formation of sugar from glycogen; it is difficult to distinguish it from glycogen; it has the same empirical formula, and gives the same colour with iodine; it, however, unlike glycogen, forms a clear solution with cold water. Limpricht found it in horseflesh; but more extended observations by Nasse 2 have shown that its amount is variable and dependent on the stage into which the glycogen has been transformed after death.

Maltose. It is Nasse chiefly who has worked at the transformation of glycogen into sugar. During activity and at certain stages after death the glycogen certainly diminishes in quantity, and it is believed to be changed into sugar and, according to Nasse, partly also into lactic acid. Reasons have, however, been advanced on p. 409 which show that lactic acid is probably derived from the proteids of the muscle, not from its carbohydrates. From resting muscle little or no sugar can be obtained. According to Meissner 3 the sugar which is formed on activity is not dextrose but maltose.

Inosite. This substance, which is isomeric with dextrose but is non-fermentable, does not reduce copper salts, and has no action on the plane of polarised light, was first discovered by Scherer in the heart of the ox, and has since been found in the voluntary muscles in small quantities (0-03-0008 per cent. [Limpricht, Jacobsen]), and in unstriated muscles (Lehmann). Inosite is also found in other animal tissues and in many plants. It crystallises in colourless monoclinic tables (C6H12O6+2H2O), and when pure gives with nitric acid and calcium chloride a pink colour (see p. 100).

Alcohol. Small quantities of ethyl alcohol were found by Rajewsky in the fresh muscles of the rabbit, ox, and horse. Béchamp confirmed this observation.

Lactic acid. The question of the method of the formation of lactic acid has already been discussed in connection with rigor mortis

1 E. Krauss, Virchow's Archiv, exiii. 315.

5 Meissner, Göttinger Nachrichten, 1861, p. 206, and 1862, p. 157.

2 Loc. cit.

+ Scherer, Ann. Chem. Pharm. lxxvii. 322. For the most recent account of the chemical constitution of inosite see Maquenne, Compt. rend. vol. civ. (1887), pp. 225, 297, 1719, 1853.

S Pflüger's Archiv, xi. 122.

Compt. rend. xxxix. No. 13.

(see p. 409), and the opinion has been advanced that it is formed from proteid, not from carbohydrate. This acid is produced during both the contraction and the death-rigor of muscle.

We have already seen that there are two isomeric lactic acids (C3H6O3) produced; one is sarcolactic or para-lactic acid (optically active ethidene lactic acid), and the other is ethene lactic acid. We have still to describe the preparation and distinctive properties of these acids.

Preparation. The syrupy liquid from which creatine has crystallised (Liebig's method, see p. 419) is acidulated with sulphuric acid and extracted with ether. The ether contains the lactic acids in solution; it is evaporated to dryness and the residue dissolved and boiled in water in which carbonate of zinc is suspended. It is then filtered, and the filtrate evaporated to a small bulk. On treating this with absolute alcohol, the liquid deposits needles of zinc sarcolactate, the ethene lactate of zinc remaining in solution. The sarcolactate is filtered off, and the filtrate evaporated down, when the ethene lactate separates out. This also is filtered off. We thus have zinc sarcolactate on one filter, and zinc ethene lactate on another. The free acid is prepared from each in the same way. The crystals of the zinc salt are dissolved in water; sulphuretted hydrogen is passed through the solution; the zinc sulphide is filtered off; the filtrate is concentrated, shaken with ether, and, on evaporating the ethereal extract to dryness, the free acid is obtained.

has

3. Calcium compound
the formula

3. Calcium compound has the formula 2[Ca(C,H,O,).] +9H,O. Specific rotation = | Ca(C ̧H ̧Ó ̧)1⁄2+5H,O. Op-3.8°.

tically inactive.

4. When oxidised with dilute chromic acid, acetic and formic acids are produced. At 100° lactic anhy

with

4. Oxidised dilute chromic acid, ma

dride (CHO) and at 140° lactide (C,H,O) are lonic acid (C,H ̧0,)

formed.

produced. Lactic anhy dride and lactide are formed as in the case of the two other acids.

Quantity of lactic acid in muscle.-This is variable; the various analyses that have been made give numbers varying from 01 to 10 per cent. (Jacobsen, Takacs, Böhm, Demant).

Fat. A certain quantity of fat is always present between the muscular fibres; it is not possible to say whether any of the fat obtained from muscle comes from the muscular substance proper or

not.

There are two conditions, however, in which fat is undoubtedly present :

1. In the affection known as fatty degeneration, the interior of the sarcolemna becomes crowded with fat granules and globules; these first obscure and finally obliterate the striations of the contractile substance. It often occurs markedly in the heart; it may be produced artificially by certain poisons, especially by phosphorus.

2. After death the muscular substance may be replaced by a waxy material, known as adipocere. This occurs especially in corpses buried in damp soil, or in bodies which remain in water some time after death. The length of time after death that these changes occur has been the subject of extended observations, especially at the Paris Morgue; it is found to occur in the muscles in a definite order, and the amount of adipocere present is a very good gauge of the time a body has been dead. Adipocere consists chiefly of the calcium soaps of palmitic and stearic acids, and, in some cases, of acid ammonium soaps also. Hoppe-Seyler 3 regards the change as a result of a ferment action.

The formation of fat from proteids probably occurs under other circumstances; for instance, fat is formed in the body on an exclusively proteid diet.

Inorganic Constituents of Muscle

The most noteworthy points in the inorganic constituents of muscle are the predominance of potassium over sodium among the bases, and of phosphoric acid among the acids. This appears to be a general rule throughout the animal kingdom. The total amount of ash is from 1 to 1.5 per cent.

4

The following analyses are by Bunge1:

1 See more fully in works on Forensic Medicine.

* Quain, Med. Chir. Trans. 1850, 141. Virchow, Verhandl. d. phys. med. Gesellsch. zu Würzburg, vol. iii. Wetherill, Journ. f. prakt. Chem. vol. lxviii. p. 26. K. B. Lehmann, Bied. Centralbl. 1889, p. 66. 5 Physiol. Chem. P. 119. Bunge, Zeit. physiol. Chem. ix. 60. Other analyses will be found in Hoppe