200. Fish have been generally considered as holding a middle rank between the flesh of warm-blood animals and vegetable food. It is certain that they are less nutritive than mutton or beef; but the health and vigour of the inhabitants of fishing-towns evidently prove that they are sufficiently nourishing for all the purposes of active life: but in order to satisfy the appetite, a large quantity is requisite; and the appetite returns at shorter intervals than those which occur during a diet of meat. Nor does this species of food produce the same stimulus to the body; the pulse is not strengthened as after a repast of flesh; and that febrile excitement which attends the digestion of the more nutritive viands is not experienced. Hence fish afford a most valuable article of diet to invalids labouring under particular disorders; for it furnishes a chyle moderately nutritive, but, at the same time, not highly stimulant. From the nature of their texture, they do not require a laborious operation of the stomach; although sufficiently solid to rescue them from those objections which have been urged against liquid or gelatinous food.

From the observations just offered upon the nutritive powers of fish, it must follow, that such a diet is not calculated to restore power to habits debilitated by disease, and should never be directed under such circumstances, but from the conviction that the digestive powers are unable to convert stronger aliment into chyle. The jockeys who waste themselves at Newmarket, in order to reduce their weight, are never allowed meat, when fish can be obtained. On account of the low stimulant power of fish, they require the assistance of condiment; and on this account salt appears to be an essential accompaniment.

201. Fish have been arranged under three divisions; viz. fresh-water fish, salt-water fish, and shell fish. But, since the value of these animals as articles of food has an intimate relation to the colour and texture of their muscles, and to their gelatinous or oily qualities, it will be expedient to consider their several varieties, with reference to such conditions. Turbot, cod, whiting, haddock, flounder, and sole, are the least heating of the more nutritive species; and the flakiness of the fish, and its opaque appearance after being cooked, may be considered as true indications of its goodness; for when the muscles remain semi-transparent and bluish, after sufficient boiling, we may reject it as inferior in value, or not in season. When the fish is in high perfection, there is also a layer of white curdy matter, resembling coagulated albumen, interposed between its flakes. The whiting ("the chicken of the sea") is well adapted for weak stomachs, on account of the little viscidity which it possesses; it is, at the same time, tender, white, and delicate, and conveys sufficient nutriment, with but little stimulus, to the system. The haddock much resembles it, but is firmer in texture.

Cod has a more dense fibre than the two former, and contains also more glutinous matter: it is an excellent aliment, but, upon the whole, is not quite so digestible as whiting or haddock. It is generally preferred when large; but such fish are frequently coarse. The haddock is certainly better when it does not exceed a middling size. A process called crimping is sometimes adopted, for the purpose of improving cod and some other fish. Sir Anthony Carlisle has investigated the change thus produced; and we are indebted to him for some curious observations upon the subject. Whenever the rigid contractions of death have not taken place, the process may be practised with success. The sea fish, destined for crimping, are usually struck on the head when caught, which, it is said, protracts the term of this capability; and the muscles which retain this property longest are those about the head. Many transverse sections of the muscles being made, and the fish immersed in cold water, the contractions called crimping take place in about five minutes; but if the mass be large, it often requires thirty minutes to complete the process.

It has been found that the muscles subjected to this process have both their absolute weight and specific gravity increased; whence it appears, that the water is absorbed, and condensation produced. It was also observed, that the effect was always greater in proportion to the voraciousness of the fish. The object, therefore, of crimping, is to retard the natural stiffening of the muscles, and then, by the sudden application of cold water, to excite it in the greatest possible degree; by which means the fish acquires its natural firmness, and keeps longer. The operation certainly improves the flavour, as well as the digestibility of the fish. Turbot is an excellent article of food; but it is usually rendered difficult of digestion by the quantity of lobster sauce with which it is eaten. Sole is tender, and yet sufficiently firm; it is, therefore, easy of digestion, and affords proper nutriment to delicate stomachs. It is necessary to state, that every part of the same fish is not equally digestible; and it unfortunately happens, that those which are considered the most delicious are, at the same time, the most exceptionable: the pulpy, gelatinous skin of the turbot, and the glutinous parts about the head of the cod, are very apt to disagree with invalids.

Salmon may, perhaps, be considered the most nutritive of our fish; but it is heating and oily, and not very digestible: and persons, even with strong stomachs, are frequently under the necessity of taking some stimulant to assist its digestion. The addition of lobster sauce renders it still more unwholesome: the best condiment that can be used is vinegar. As connected with the time of spawning, the season of the year has the most decided influence upon the quality of salmon. It is in the highest perfection, or in season, as it is termed, some time previous to its spawning; the flesh is then firm and delicious: whereas, after this event, it is for some time unfit for food. This circumstance, however, is not sufficient to prevent those who have an opportunity, from catching and eating the fish in that state; and the legislature has accordingly found it necessary to fix the periods at which salmon fishing is lawful. In Ireland, where there is great freedom used in killing salmon, during and after the spawning season, the eating of the fish at such times has been often found to be productive of disease; and Dr. Walker has related a circumstance of the same kind as having occurred in Scotland. Salmon trout is not so rich and oily as the salmon; although, therefore, it is less nutritive, it is, at the same time, less heating and more digestible.

Eels are extremely objectionable, on account of the large proportion of oil which they contain. I have witnessed several cases of indigestion and alimentary disturbance from their use. When eaten, they should always be qualified with vinegar. From these observations, the value of fish may be appreciated, and the qualities which entitle them to election easily understood. Firmness of texture, whiteness of muscle, and the absence of oiliness and viscidity, are the circumstances which render them acceptable to weak stomachs.