Exposed to the action of water, the muscle undergoes different phenomena, according as it is hot or cold. Cold water takes from it at first its red colour, of which it appears to dissolve the principle. To effect quickly this phenomenon, it is necessary to expose the flesh, at first in thin layers, to the action of water that is often changed, by placing a muscle for example under a fountain, in the current of a river, or what is much better, by frequently expressing the water it imbibes; for if we keep it in a vessel, its exterior only whitens a little, and the interior preserves its colour. Water which has been used to wash a muscle, looks like blood spread out in this fluid; it contains the colouring matter, a little of the extractive substance, gelatine, &c. I believe that of all the organs the muscle is that from which we remove most easily its colour by artificial means. Ought we to be astonished after this, if nature varies so evidently and so frequently this colour by the phenomena of nutrition, as we soon shall have occasion to remark? Kept in water at a moderate temperature, the muscular texture remains for a long time without softening; it finally does, and changes layer by layer into a kind of putridity very different however from that which is formed in the open air, as I have frequently observed in macerating the muscles in a cellar, the temperature of which is uniform. At other times, instead of putrefying thus, the muscle is changed, as Fourcroy has remarked, into a substance like spermaceti; then its fibre is hard and solid. But all the muscles when kept in water by no means exhibit this phenomenon. When it does take place, very often a kind of reddish product, scattered here and there on the surface of the muscle, and which is an evident effect of decomposition, announces and afterwards accompanies this state, without which also, it often takes place. Maceration in dissecting rooms frequently exhibits this phenomenon.
When we have taken from the muscles their colouring substance by repeated washings, there remains a white fibrous texture, from which we can still extract albumen by ebullition, which rises in scum, gelatine by suffering it to grow cold, extractive matter which has a deep colour, by letting it settle, and some phosphoric salts. When all these substances have disappeared, the residue of the muscle is a fibrous substance, of a greyish colour, insoluble in warm water, soluble in the weak acids, giving out much azote from the action of the nitric acid, and presenting all the characters of the fibrin of the blood. It appears, as Fourcroy has remarked, that this substance is truly the nutritive substance of the muscle, that which, continually exhaled and absorbed, contributes to its nutritive phenomena more than all the others; it constitutes the essence of the muscle, it especially characterizes it, as the phosphate of lime is the nutritive characteristic matter of the bones. Is this substance formed in the blood and carried from it to the muscle, or is it formed in the muscle by nutrition, and thence carried to the blood? I know not. Whichever may be the case, it appears to experience very great varieties in its exhalation and absorption. The state of laxity, of cohesion, the thousand various appearances of the muscular texture, appear to belong in part to these varieties of proportion. Thus the phosphate of lime or gelatine, diminished by nutrition, give to the bones softness or brittleness.
It is in this fibrous and essential portion of the muscle, that particularly resides the faculty of crisping by the action of caloric, whether by plunging a muscle into boiling water, or exposing it to the fire; for this crisping is as evident in the muscle deprived of its colouring matter, its gelatine, its albumen, and even a portion of its extractive substance as in the ordinary muscle. There is in general a constant relation between the quantity of this fibrous substance contained in the muscles, and the quantity that the blood contains of it. In the strong, vigorous, sanguineous temperaments, as they are called, the muscles are thick and much more fibrous. In all the slow cachexiæ in which the blood is impoverished, the pulse small and feeble and in which muscular nutrition has had time to share but little of the fibrin of the blood, the muscles are small, weak, soft, &c. In general, the muscles and the blood are always in constant relation, whilst other systems often predominate and whilst this fluid seems to be in less quantity in the economy.
Exposed for a long time to ebullition, as in common boiled meat, the muscular texture, still united to the adjacent organs, and to its common parts, gives, 1st, an albuminous scum which appears to arise more from the lymph of the cells than from the muscle itself; 2d, many fatty drops coming also especially from the cellular texture, almost foreign consequently to the texture of the muscle, and which swim on its surface; 3d, gelatine formed especially by the aponeurotic intersections; 4th, an extractive substance which colours in part the water in which it is boiled, gives it a peculiar taste and remains in part adherent to the flesh to which it communicates a deep tinge wholly different from that of raw flesh, a tinge which arises also from the colouring matter of the muscle, and which moreover changes, when the liquor cools, into a less deep and even a whitish tinge; 5th, various salts which contribute much to the taste of the liquor, and the nature of which chemists have ascertained. These are the natural phenomena of the ebullition of the muscle.
The more extensive analysis of boiled flesh is not my province; but what ought not to escape us here, are the phenomena of which the fibre is the seat, whilst the preceding products are extracted, whether from it, or the surrounding textures. These phenomena can be referred to three periods. 1st. When the water is only tepid, and even a little above the temperature of the body, it leaves the muscular texture in the same state, or softens it a little. 2d. When it approaches ebullition and begins to be covered with an albuminous scum, the texture crisps, thickens and contracts and gives to the muscle a density much greater than what is natural to it, and augments considerably its resistance. I have observed that in this state the muscles bear much greater weights than in a natural state. They approximate, if we may so say, that remarkable density which characterizes them when they contract in the living body, and which so powerfully opposes their rupture. This condensation of the muscular texture, which is prompt and sudden, increases till the period of ebullition, when it is at its greatest height; it continues only for a certain time. 3d. Gradually it diminishes, the fibres soften, and are more easily torn than in their natural state. This softening, the reverse of the hardening that precedes, is produced slowly and by degrees. When arrived to a certain degree, the meat is rendered fit for the table. Observe that then the muscle has not returned to the state in which it was found before the hardening; among other phenomena which distinguish it, the following is an essential one; it has lost the power of crisping, of acquiring the horny hardness, from the action of the concentrated acids, from alkohol or from caloric. In general it becomes putrid more slowly. Its putrefaction does not give the same odour. We know how much its taste differs. The principles it has lost are undoubtedly one of the great causes of these differences.
When a muscle is exposed to an open fire, as in the roasting of meat, the albumen is condensed, the gelatine melts, the fibrin filled with juices softens, the extractive matter flows in part with the gelatine and the salts held in solution; it is this that forms the gravy, which is, as we know, very different from melted fat. The exterior of the meat remains more dense than the interior; it is coloured by the extractive substance. The interior loses in part its natural colour; its consistence, its taste and its composition even change entirely. The fibres, as in ebullition, lose the power of contracting and of crisping from the action of strong stimuli and especially that of fire.
No part in the animal economy is more easily altered by the digestive juices than the muscles. Almost all stomachs can bear boiled meat, whilst many reject other organs when cooked. Carnivorous animals seize upon the muscles of their prey in preference to the pectoral and gastric viscera. Muscular flesh is with most people the most common aliment, that with which they are never disgusted; it appears to be the most nourishing of all those, which are afforded by the different textures of animals; is it, as it has been said, because it contains the most azote? Whatever may be the reason, the general part which the muscular system takes in the digestion of all carnivorous animals, of man especially, is remarkable. Yet all the parts of this system do not appear to be equally agreeable to the taste of animals. It is, for example, a singular fact, that those bodies which are brought to our dissecting rooms, and which have been attacked by rats, are found almost always exclusively gnawed in the muscles of the face.
Observe in regard to the use of the muscles in digestion, that it is the portion of the fibrous system which adheres to them, and forms, as it were, a part of them, I refer to the tendons, which is the most easily altered by maceration, by ebullition and by the digestive juices. Observe also that the great mass which the muscles form in the body of all animals, of which they are more than one third, presents to the carnivorous species ample materials for their nutrition; thus nature, by multiplying these organs for the wants of the individual which they move, seems to multiply them also for those of the individuals which he is one day to nourish. In forming them in each species, it labours for other species as well as for this. Who knows if this general design, which observation finds in the series of all animals, be not the cause of this remarkable predominance which the muscles have over the other systems? Who knows, if nature would not have diminished the powers of the animal mechanism which are so numerous and so complicated in comparison with those of artificial machines, who knows if she would not have simplified the means and given the same results, if the motions of the animals had been the only object of the formation of the muscles?
The sex has great influence on the quality of the flesh of animals. I do not believe that any thing precise is known as to the nature of the influence which the genital parts exert upon it; but the following are remarkable facts upon this subject. The muscles of males are stronger and better nourished, have more taste, resist boiling for a longer time, are firmer, &c. Boiling water on the contrary alters quicker the texture of females; it is more tender and gives to the liquor a less strong taste. In the season of sexual intercourse, the muscular system of the first has a peculiar odour, which often renders it disagreeable even to the taste. It is an observation that is easily made in quadrupeds, birds and fishes that are brought to our tables. Without having as strong an odour, the flesh of the second becomes at this period soft, flaccid and but little savoury.