CHAPTER XII ANIMAL AND FISH FOODS E. H. S. BAILEY, PH.D. Blessed art thou, O land, when thy King is the son of Nobles, and thy Princes eat in due season, for strength, and not for drunkenness.-Ecclesiastes x, 16-17. Meats; Meat Extracts; Gelatin and Gelatin Foods; Animal Viscera as MEATS Importance of Meat.-Meat is one of the most important foods, since it is from animal flesh that the muscular part of the body derives its sustenance. It is the chief source of our protein supply. Fats, carbohydrates, water and mineral salts are other constituents of various meats. This class of food is easily digested, either cooked or in the raw state, after thorough mastication. Meat mixes readily with all other foods and leaves but a small residue in the intestinal canal. COMPOSITION OF MEAT.-On close inspection, a piece of boiled meat will be found to be made up of bands of muscle fibers held together by connective tissue. These muscle fibers may be short, as in the breast of a chicken, or they may be much longer, as in the leg of a crab; the shorter they are, the more tender and easily digested the meat is. Meat should always be carved at right angles to the long axis of the fibers. It is then masticated with greater ease. The contents of the muscle fibers. are more readily brought into contact with the grinding surface of the molars, the taste and flavor are increased and the digestive juices stimulated, facilitating the process of digestion. FAT.-The walls of the muscle fibers consist of an albuminoid substance, elastin, while the connective tissue which holds them together is composed chiefly of a material called "collagen," which yields gelatin on boiling. Imbedded in the connective tissue between the fibers is a variable amount of fat. It is almost entirely absent in most kinds of game and in the breast of chicken. On the other hand, in pork and fattened mutton, in swimming birds (such as the duck and goose, which require a large store of fat both to lighten the body as well as a source of animal heat), the amount of fat may be large. A large amount of fat tends to diminish the digestibility of meat; apparently the fat forms a kind of waterproof coating around the muscle fibers, hindering their rapid disintegration in the gastric juice. Under ordinary conditions meat contains muscle tissue, connective tissue, blood vessels, nerves and lymphatics, together with a varying amount of fat. The greater the amount of fat there is in the meat, the less water and nitrogenous matter does it contain, and vice versa. MUSCLE TISSUE.-As we have already learned, muscle tissue is made up of minute thread-like cells that lie side by side and are so small that the individual cells may be seen only by the microscope. In the living animals the contents of these muscle cells are soft and tender. After death a change takes place in the muscle substance, which causes it to become rigid. This hardening of the muscle is known as rigor mortis, or death stiffening. It is due to myosin, which has the property of clotting after death. Meat in this condition is tough. If tenderness is desired the meat should be immediately cooked after the animal is killed, before this condition of rigor mortis has had time to set in. If, however, the animal is allowed to hang for a time, this rigor passes off. Its disappearance is due to a resolution of the myosin by the development of sarcolactic acid and acid phosphates in the tissues, as well as to a partial digestion of it by traces of pepsin, which all muscle fiber contains. This process must be regarded, however, as an early stage of putrefaction, and, as is well known, if meat is allowed to hang for some time it becomes high. ACIDS. The acids which develop in meat after the disappearance of rigor mortis aid the gelatinization (which occurs in boiling) of the connective tissue, and also improve its flavor by changing the rather insipid taste, which characterizes very fresh meat, to one more palatable. Animals which have undergone very great muscular exercise immediately before killing develop a considerable quantity of these acids, hence the flesh of hunted animals is of a superior flavor. Another means of pro ducing these effects artificially is by soaking the meat in vinegar and water for a short time. This improves the flavor of fresh meat, as well as its tenderness. It is on this same theory that the use of vinegar favors the digestibility of the hard muscles of the crab and lobster. MUSCLE JUICE.—The contents of the microscopic muscle fibers consist of water, holding in solution, proteins, salts and substances known as meat extractives, the whole constituting muscle juice. The younger the animal the more water does its flesh contain, and likewise the lower its nutritive value. This is explained by the saying that "calf meat is half meat." MINERAL SUBSTANCES.-We learned when studying mineral salts that the red coloring matter of the meat was due to the presence of hemoglobin, which varies greatly in different kinds of meat. Its greatest importance is that it contains iron. In the small blood vessels of animals which have bled to death, hemoglobin may be found much diminished in amount or altogether removed. The chief mineral substances found in the juice of meat are phosphoric acid and potash. Meat is one of the principal sources of these valuable building materials in the diet. When these are not supplied in sufficient amount, the muscles become flabby and poorly developed. ACCESSORY SUBSTANCES-VITAMINES.-Besides protein, fat and mineral substances, fresh meat contains certain accessory substances which are of importance to the animal organism. Cured and dried meats are deficient in these substances. Casimir Funk described them first and gave them the name vitamines. The leading investigators are of the opinion that meat vitamines are contained in the plasma or muscle juice, and that they form the preventative and curative agents in raw meat and raw meat juice. No doubt the efficacy of raw meat juice as a curative agent in tuberculosis lies in the vitamines of the muscle plasma. This curative property is not due to proteins, for it has been shown that muscle plasma contains very little nitrogen. Whatever the organic principle may be, it is destroyed by prolonged cooking, for neither cooked meat. nor cooked meat juice possesses the therapeutical effects of raw meat juice. The destruction of vitamines by heat depends on the height of the temperature to which the meat is subjected. It is generally believed that a temperature of 120° C. destroys vitamines, but at this temperature the interior of a cut of meat weighing 5 or 6 pounds never reaches more than 60° C. during ordinary cooking. The vitamines contained in the meat juice of fresh meat are a protection against scurvy and beri-beri. Grijns (1) was an early worker in this field, and his conclusions are that the vitamines of meat are destroyed when heated to 120° C. It was due to his research that the deficiency theory of beri-beri was adopted. He believes that the disease breaks out when this substance, necessary for the metabolism of the nervous system, is lacking in the food. Grijns avers the condition frequently alluded to as nitrogen starvation may exist even when the vitamines are abundant, and has no relation whatever to the condition that Funk refers to as deficiency diseases. Yet individuals in a condition of nitrogen starvation are likely to suffer from deficiency of vitamines and therefore furnish a large percentage of cases of scurvy, beri-beri and pellagra. They are cured by any food containing vitamines. Their nitrogen defect is not relieved unless proteins are also administered. It is believed that a diet defective in vitamines weakens our acquired immunity to tuberculosis and that the rich diet prescribed of late years cures by reason of the excess of vitamines, rather than solely by the nitrogen administered. EXTRACTIVES. The principal substances contained in a solution of meat juice are the extractives. They are so called because they may be extracted from meat by boiling it in water. We shall have much to learn about these extractives later on, but it may be stated here that their exact chemical nature is not definitely known, neither have they any nutritive value. They are of importance only because they give the agreeable and characteristic taste to meat. Meat from which these extractives have been removed by prolonged boiling becomes flavorless and insipid. The flesh of adult animals is richer in extractives, has a richer flavor than the flesh of those which are immature. This explains why we eat lamb with mint sauce and add spices to veal. The influence of feeding and pasturage is well illustrated by all forms of game. The flesh of wild rabbits, which eat aromatic herbs, for instance, has a much finer flavor than that of rabbits fed in captivity. For this same reason a portion of wild turkey or wild duck is admitted to be a more tasty morsel than the flesh of birds reared in a farmyard. Everyone knows the fishy taste of sea birds, and that mutton raised in the hills is superior to its turnip fed substitutes. CHEMICAL COMPOSITION OF MEAT.-The chemical composition of meat varies somewhat with the particular cut and the degree to which it has been fattened. The ordinary butcher's meat does not consist entirely of edible matter. In an average piece of meat the waste may be safely reckoned at fifteen per cent of the whole and the proportions of the constituents of the edible part are about as follows (König): Other analyses represent the proportions of the chemical substances present, thus: The effects of fattening are shown in the following table, in which the composition of lean, medium and very fat beef is stated in round numbers: Note the high percentage of water in meat as compared with the other constituents, the weight of the water contained is three times that of the nutritive parts. In other words, each pound of meat consists of threequarters pound of water and one-quarter pound of nutritive material. The meat from young animals contains the highest percentage of water. Another interesting point shown by the above table is the relation between water and fat. These constituents vary in inverse ratio, the more fat there is, the less water is present. To sum up: fat replaces water in muscular tissue, the protein elements being unaffected. Therefore, by the fattening process the nutritive value of the meat is absolutely increased. The above analyses refer especially to beef; the composition 1 "Nitrogenous matter" is the figure obtained by multiplying the amount of nitrogen in 100 parts by 6.25; i.e., it is assumed that it is all protein. In reality, 15 per cent of the total nitrogen is present in the form of extractives, the amount of which can be calculated by multiplying their nitrogen by 3.12. |