For some time after death, the muscular parts of animals continue to suffer contraction, followed by relaxation, when stimulated, as by the point of a needle, or the application of Galvanism. But this irritability or organic contractility, as it is termed by some modern physiologists, gradually disappears in the different organs, and commonly in the muscles of the trunk, before those of the limbs. It is also observed, that, in the different classes of animals the duration of the irritability is inversely as the energy of muscular action which they exhibit during life. It is strongest and most durable in animals which are suddenly killed when in high health, and is weak and evanescent in those which die of linger. ing diseases, or from fatigue.
After the irritability has entirely ceased, the mus cles begin to become rigid, first those of the trunk, and then those of the limbs. Its duration is inverse ly as of its commencement; and it is long. est of beginning, but is greatest and lasts longest in those animals which are suddenly killed when in high health. It appears very quickly, and lasts a short time only, in animals which die of exhaustion, or from fatigue. In whatever attitude the limbs are placed at its commencement, they continue; and hence butchers take care to dress properly the car. cases of animals while yet supple. For after rigidity has commenced, if the position of the limb be for cibly changed, it is destroyed, and the joint becomes permanently supple. Also muscles which are frozen, when rigid, are extremely supple as soon as they are thawed. Rigidity is perhaps never developed in ani. male; frozen-to death. • While this rigidity continues, the flesh of animals is hard and stringy, and, so far as the palate is concerned, not yet fit for the table, although fully nutritious, and in perfection for making soup. After the rigidity has totally ceased, animal flesh is not long of experiencing the commencement of those chemical changes, which terminate in putre faction; and it is of the utmost importance, in do• mestic economy, to take care that all large joints be in this intermediate state when they are cooked ; for no skill in the culinary art will compensate for negligence in this point, as every one must have often experienced to his great disappointment. Meat, in which we are able to detect the slight est trace of putrescency, has reached its greatest de. gree of tenderness, and should be used without de lay ; but before this period, which in some kinds of meat is offensive, the degree of inteneration may be known by its yielding readily to the pressure of the 'finger, and 'by its 'opposing little resistance to an at bend the joint. Poultry also thus part y with their feathers, and it would be advisa ble to leave a few whenahe bird is plucked, in or tier to assist in determining their state. " No man
who understands good living will say, on such a day will I eat that turkey, but let him hang it up by four of the large tail feathers, and when, on paying his morning visit to the larder, he finds it lying up en a cloth, prepared to receive it when it falls, that day let it be cooked." But as we cannot always choose our time for eating the joints in our larder, we must, in providing them for a particular day, es timate 'that they will then be in a proper state, or, if necessary, endeavour to hasten or retard it. By experience, we acquire some knowledge of the length of time for which the different kinds of meat should be kept, although it is subject to great variations, depending upon the temperature, moisture, and ven tilation of where it is kept, upon the kind of meat, the age of the animal, and upon peculiari ties in the individual not understood.
The chief means of preventing the fermentation of organic substances are reduction of temperature, desiccation, exclusion of air, and the action of cer tain substances called antiseptic. Although most commonly employed in combination with each other, we shall briefly explain the principles upon which they act singly, and then notice their practical ap plication in reference to the animal and vegetable kingdoms.
A moderate reduction of temperature acts by re tarding vital and chemical action, and a reduction, capable of freezing the juices and fluids of organiz ed bodies, by destroying vitality, and converting the water present into ice, and thus removing a con dition essential to chemical action. Many vegeta ble, and some animal substances, such as eggs, pos sess what may be called latent life, and so long as this continues they resist fermentation. A very low temperature puts an end to it, while a high temper ature calls it into action, after which it cannot be sus pended without destroying it altogether, and thus it is longest preserved in a temperature just a little higher than the former. An egg which has been frozen is killed, and rots soon after being thawed. On the other hand, by incubation, or an equal de gree of heat, the life of the chick becomes active, and cannot again be checked with impunity ; while; at a moderate low temperature, the latent life of an egg continues a great length of time, ready to be excited into action when placed in favourable cir cumstances, and resisting the natural tendency to chemical change. The same observation nearly ap plies to vegetables. Succulent roots, for example, can be long preserved in a moderately low temper ature, but if it be raised they begin to shoot; or if it be reduced too much, they die and soon rot.