Popular Science Monthly/Volume 35/May 1889/Eggs in Chemistry and Commerce



WHAT a subject scientific research has found in eggs as a study, witness the works of Moquin-Tandon and O. des Murs.[1] These publications serve to show how the oölogic characteristics may assist in the methodical classification of birds, what relation there is between the egg and the organic conformation of the bird, and what particular habits of birds may be gathered from a study of their eggs and nests.

Some birds only lay a single egg, others many. The largest ordinary number, on the average, is five or seven. The species laying less are more rare than the species laying a larger number. Those in a state of liberty produce, on the average, twelve to fifteen. But in domestic poultry the number is larger. Farmyard hens average sixty or seventy eggs in the year, and certain Cochin-China fowls are said to lay from two hundred to three hundred eggs. The number of eggs laid is less at the commencement and end of life. With hens, for instance, the number laid is less in the first and fourth year than in the second and third, and after the fifth year, generally, they cease laying. Chickens and ducklings, which can generally shift for themselves soon after emerging from the egg, are more numerous in a brood than young pigeons, which have to be fed by the parent. But if pigeons only lay two eggs at a time, they lay more frequently—once or twice a month—and hence rear a large number of young.

In form and general aspect the difference among birds' eggs is endless. Some are elongated, some are spherical, some are dull on the surface, some are polished, some are dark, others gray or white, others very bright. The shape of eggs offers as much diversity as their size and weight. They may be thrown, however, into six principal or typical forms—the cylindrical, the oval, the spherical, the ovicular, oviconical, and the elliptic. The ovicular form of egg belongs to the Passeræ and Gallinaceæ, the ovoid to the rapacious birds and the Palmipedes, the conical to the wading birds and some Palmipedes, the short to some game and many stilted birds, and the spherical to nocturnal birds of prey and the kingfishers.

Mr. W. C. Hewitson observes that in their relative sizes the eggs of different birds vary in a remarkable degree from each other. The guillemot and the raven are themselves about equal in size, but their eggs differ as ten to one. The snipe and the blackbird differ but slightly in weight, their eggs remarkably. The egg of the curlew is six or eight times as large as that of the rook; the birds are about the same size. The eggs of the guillemot are as big as those of an eagle, while those of the snipe equal the eggs of the partridge and the pigeon. The reason of this great disparity in size is, however, obvious. The eggs of all those birds which quit the nest soon after they are hatched, and are consequently more fully developed at their birth, are very large, and yet so admirably formed to occupy the least possible space, that the snipe has no more difficulty in covering its eggs, though apparently so disproportionate, than the thrush or the blackbird. Hence we see that eggs are not always proportioned to the size of the birds which lay them. The standard yield and weight of eggs for the different varieties of domestic fowl are about as follow: Light Brahmas and partridge Cochins, eggs seven to the pound; they lay, according to treatment and keeping, from eighty to one hundred per annum, oftentimes more if kept well. Dark Brahmas, eight to the pound, and about seventy per annum. Black, white, and buff Cochins, eight to the pound; one hundred is a large yield per annum. Plymouth Rocks, eight to the pound, lay one hundred per annum. Houdans, eight to the pound, lay one hundred and fifty per annum; non-sitters. La Flèche, seven to the pound, lay one hundred and thirty per annum; non-sitters. Black Spanish, seven to the pound, lay one hundred and fifty per annum. Dominiques, nine to the pound, lay one hundred and thirty per annum. Game fowl, nine to the pound, lay one hundred and thirty per annum. Crèvecoeurs, seven to the pound, lay one hundred and fifty per annum. Leghorns, nine to the pound, lay from one hundred and fifty to two hundred per annum. Hamburgs, nine to the pound, lay one hundred and seventy per annum. Polish, nine to the pound, lay one hundred and fifty per annum. Bantams, sixteen to the pound, lay sixty per annum. Turkeys, eggs five to the pound, lay from thirty to sixty per annum. Ducks' eggs vary greatly with different species, hut from five to six to the pound, and from fourteen to twenty-eight per annum, according to age and keeping. Geese, four to the pound, lay twenty per annum. Guinea fowls, eleven to the pound, lay sixty per annum. Large eggs have generally a thicker shell than small ones. By comparison with eggs in former times, those of improved breeds of fowls of the present day have gained one third in weight.

Exceptionally large hens' eggs are often met with. Thus, in the journal "Land and Water" for June 16, 1877, a Cochin-China fowl's egg is recorded which weighed one quarter of a pound and measured eight and five eighth inches lengthwise, six and a half inches in circumference. That of a Dorking weighing seven ounces measured seven and a half inches round the middle and nine and a half inches across the ends. Another weighed ten and a half ounces, and measured eight inches round the center and twelve and a half inches across the ends.

In the "Birmingham Mercury" of May 9, 1857:

A half-bred Cochin-China hen belonging to Mr. Campbell, carter, of Great Croft Street, Darlaston, is stated during the past few weeks to have laid eleven extraordinary eggs of an enormous size, each weighing upward of five ounces, and one when just laid weighed not less than seven ounces. On one being broken another perfect egg, of the usual size, was found inside, which led to seven being broken with the same results. Around the one weighing seven ounces (being the tenth egg) a third shell and egg had begun to form. Several of these eggs are whole, and by carefully handling them the motion of the inner eggs may be perceived. Two of the inner eggs are also preserved, and numbers of people have been to see them, and have expressed themselves highly gratified at such an extraordinary phenomenon. The hen is not above the middle size, being about four and a half pounds in weight.

Many eggs are laid naked, dry, and smooth; others are impregnated with a greasy, glutinous substance. The latter are chiefly those of sea-birds, or those which live in moist localities. This glutinous coating is doubtless intended to preserve the eggs from the water, or to maintain the degree of heat necessary to preserve life. There are soft eggs laid entirely without shells, or with only the albuminous inner membrane. This occurs chiefly in hens that are too fat; and this failing can be remedied by supplying calcareous substances with their food.

Egg-shell is much used in medical prescriptions. When calcined at a low red heat the shells afford a very pure form of carbonate of lime. The principal use of egg-shells is, however, when blown, for the cabinets of private ornithological collections and those of public museums. The eggs of the ostrich are often mounted in silver, and form elegant drinking-cups; so are the handsome green eggs of the Australian emeu, which look as if made of dark morocco-leather. Ostrich egg-shells serve as water vessels among the African women; necklaces made of pieces of egg-shells punched out in a circular form are worn by some African natives.

Eggs blown are sometimes used in shooting-galleries, strung as a mark or target. The smooth surface of the egg-shell can even be used for artistic purposes, and we often see ostrich-eggs and hens' eggs painted or engraved with fanciful designs.

The employment of egg-shells for ornamental purposes is extremely ancient. A MS. in the Harleian collection represents a number of egg-shells ornamented in the most elegant and costly manner; miniatures were often painted upon them with extreme care, and egg-shells thus curiously decorated became valuable and highly esteemed presents. In Venice young noblemen frequently lavished large sums of money upon portraits painted within egg-shells, intended as presents.

Those who have only seen the ordinary fowl's eggs of our shops and poultry-yards would suppose that eggs were always white. But, on examining a large collection of birds' eggs, it will be found that they are of all colors. Except, perhaps, some very clear shades, the yellow for instance, none are wanting. There are blue eggs, yellowish, green, reddish, and olive. When we consider the eggs of some nine thousand different birds known, we find that not one fifth of those of the European birds are white, and among the exotic birds the number of white is much less. The white color is not always pure; there are gray and yellow shades, more or less of a dirty hue. In colored eggs, there are uniform colors and spotted colors. Although the larger number of the races of domestic fowls lay white eggs, there are some which have a yellow or nankeen tint; these are principally Asiatic birds. Birds which build open nests seem uniformly to have colored eggs, and those which, possess concealed or covered nests, white eggs.

But few of those who break the shells of the cooked eggs of our common domestic fowls at the breakfast-table ever think of the wonderful nature of the structure they crush, or of the complex chemical nature of the contents consumed as food. The white, fragile cortex called the shell, composed of mineral matter, is not the tight, compact covering which it appears to be, for it is everywhere perforated with a multitude of holes. Under the microscope the shell appears like a sieve, or it more closely resembles the white perforated paper sold by stationers. The shell of the egg is lined upon its interior everywhere with a very thin but pretty tough membrane, which, dividing at or very near the obtuse end, forms a small bag which is filled with air. In new-laid eggs this follicle appears very small, but it becomes larger when the egg is kept. In breaking an egg this membrane is removed with the shell, to which it adheres, and therefore is regarded as a part of it, which it is not. The shell proper is made up mostly of earthy materials. The proportions vary according to the food of the bird, but ninety to ninety-seven per cent is carbonate of lime. The remainder is composed of two to five per cent of animal matter, and one to five of phosphate of lime and magnesia.

If a farmer has a flock of one hundred hens they produce in eggshells about one hundred and thirty-seven pounds of chalk annually; and yet not a pound of the substance, or perhaps not even an ounce, exists around the farm-house within the circuit of their feeding-grounds. The materials of the manufacture are found in the food consumed, and in the sand, pebble-stones, brick-dust, bits of bones, etc., which hens and other birds are continually picking from the earth. The instinct is keen for these apparently innutritions and refractory substances, and they are devoured with as eager a relish as the cereal grains or insects. If hens are confined to barns or out-buildings, it is obvious that the egg producing machinery can not be kept long in action unless the materials for the shell are supplied in ample abundance.

Within the shell the animal portion of the egg is found, which consists of a viscous colorless liquid called albumen, or the white, and a yellow globular mass called the vitellus, or yolk. The white of the egg consists of two parts, each of which is enveloped in distinct membranes. The outer bag of albumen, next the shell, is quite a thin, watery body, while the next, which invests the yolk, is heavy and thick. But few housekeepers who break eggs ever distinguish between the two whites, or know of their existence even. Each has its appropriate office to fulfill during the process of incubation or hatching, and one acts, in the mysterious process, as important a part as the other.

The yolk contains water and albumen, but associated with these is quite a large number of mineral and other substances, which render it very complex in composition. The bright yellow color is due to a peculiar fat or oil, which is capable of reflecting the yellow rays of light, and this holds the sulphur and phosphorus which abound in the egg.

It is well known that from the egg all the constituent parts of the young animal are formed—its skeleton, as well as its various soft textures. Now, for the construction of the skeleton an amount of earthy matter is required which does not exist preformed in the soft contents of the egg, but has to be drawn from the shell. During the process of incubation, with the co-operation of the atmospheric air which permeates the shell, it appears that the phosphorus present in the yolk gradually undergoes oxidation, and becomes converted into phosphoric acid. This acts upon and dissolves the carbonate of lime belonging to the shell, which thus, as incubation proceeds, becomes thinner and thinner. The thinning of the shell also makes it easier for the young bird to peck its way out.

An enveloping membrane or bag surrounds the yolk, and keeps the fluid matter of which it is composed together. Being lighter than the white, it floats to that portion of the egg which is uppermost, but is kept in position between the two extremities by two processes of inspissated albumen, called chalazea, which pass to and are attached, one to either end of the egg.

  Entire contents. White. Yolk.
Nitrogenous matter 14·0 20·4 16·0
Fatty matter 10·5 . . . . 30·7
Saline matter 1·5 1·6 1·3
Water 74·0 78·0 52·0
Total 100·0 100·0 100·0

The white of egg, as this shows, contains a considerably larger proportion of water than the yolk. It contains no fatty matter, but consists mainly of albumen in a dissolved state, and inclosed within very thin-walled cells. It is this arrangement which gives to the white of egg its ropy, gelatinous state. Thoroughly shaking or beating it up with water breaks the cells and removes the ropy state.

Eggs are useful for many purposes besides food and hatching. The white of an egg has proved a most efficacious remedy for burns; seven or eight successive applications of this substance soothe the pain and effectually exclude the air from the burn. This simple remedy seems preferable to collodion, or even cotton. Extraordinary stories are told of the healing properties of an oil which, is easily made of the yolks of fowls' eggs. It is in general use among the peasants of southern Russia as a means of curing cuts, bruises, and scratches. When, as sometimes by accident, sulphate of copper, or corrosive poisons generally, are swallowed, the white of one or two eggs will neutralize the poison, and change the effect to that of a dose of calomel. Raw eggs have at all times been considered an excellent remedy for debility, on account of the phosphorus contained in them, as well as a preventive of jaundice in its more malignant form. The yolk is sometimes used as a convenient medium for forming an emulsion of the thick turpentines with water. These mixtures are used as enemata.

As a flesh-producer, one pound of eggs is equal to one pound of beef. About one third of the weight of an egg is solid nutriment, which is more than can be said of meat. Eggs, at average prices, are among the cheapest and most nutritious articles of diet. Like milk, an egg is a complete food in itself. It is also easily digested, if not damaged in cooking.

The celebrated Guinod de Reynière, who consecrated his life to studying the delicacies of the table, affirms, in his "Almanach des Gourmands," that eggs can be served in more than six hundred ways, and a book is published in London by a French cook, which gives one hundred and fifty recipes for cooking eggs. The feeble man, who has regained strength by boiled eggs for several days, will continue the same comforting food when presented in the form of an omelet, which is one of the principal food preparations made with eggs.

The flavor of eggs is much influenced by the nature of the package, for they imbibe foreign odors with the greatest readiness. Eggs brought in the same ship as oranges become impregnated with the scent and flavor of the fruit. If the cases in which they are packed are made of green wood, the eggs will be ruined. The straw in which they are packed should also be perfectly dry, or it will ferment and communicate a fusty smell to the eggs.

A raw egg beaten up in a glass of wine is recommended for vocalists for clearing their voice, and in cases of debility; and a spirit of eggs is sold which is said to be useful in impaired health or the infirmities of age, when vital energy is wanting, and as a specific for soreness of the throat. The white of eggs forms an albuminous solution, useful in diarrhœa of phlegmatic origin. To make this, beat up the white of four eggs and add a quart of water slowly, remove the froth formed, add sugar, a little orange-water, and, if necessary, a dozen drops of laudanum. This albumenized water is the best antidote to a great number of mineral poisons. The phosphorus in the egg is very good for all those who have brain-work to do. The sulphur in the yolk, as is well known, acts chemically on silver spoons, turning them black, forming a sulphide of silver that can not be removed without taking off the surface of silver, thus rapidly wearing the spoon away.

Eggs, although of animal origin, are now allowed to be eaten by Catholics during Lent. But it was not always so: formerly eggs never figured on the tables of the faithful during the fast; but, on the Saturday previous to Easter, a great quantity of eggs, held over for six weeks, was blessed and distributed among friends on Easter Sunday. They were dyed yellow, violet, and especially red, hence the origin of the red or Easter eggs. In the reigns of Louis XIV and XV, after grand mass on Easter-Sunday, pyramids of eggs gilded were taken to the cabinet of the king, who distributed them to his courtiers. The custom of Easter eggs is continued to the present time, although modified. Easter eggs are no longer blessed nor gilded to be offered to sovereigns, nor are they held over to Easter eve to receive brilliant colors. A fortnight before Easter, in the coffee-houses and beer-shops of Catholic cities, may be seen huge dishes of eggs of various colors, which are eaten by the customers with their beer. And in families a hard egg is added to the salad, after removing the colored shell.

The mutual presentation of colored eggs at Easter by friends continues in Russia and all Catholic countries. Fowls' eggs variously colored, and having flowers and other devices upon them, formed by the coloring matter being picked off, so as to expose the white shell of the egg, are a part of all the Malay entertainments in Borneo.

The eggs of the domestic fowl are the edible eggs par excellence, but many others can be utilized for food. The egg of the goose, which is larger, is inferior in quality; in districts where geese are bred they give, however, some benefit. The egg of the duck, with a smoother shell, smaller and less rounded, is of a greenish or dark white, the yolk is larger and of a deeper color than that of other poultry eggs, and the white by cooking attains a consistence like transparent isinglass. The egg of the pea-fowl or guinea-hen has a thick and hard shell, flesh-colored; the yolk is proportionally much larger than the white.

The common wild or gray lag goose is the origin of our domestic goose. It used to be common and bred in our fens in former years. The common goose begins to lay toward Candlemas, and lays from nine to eleven eggs. If well fed, she will lay thirty-five to forty eggs, and sometimes fifty, if the eggs are removed and she is not allowed to set. The turkey-hen lays from twelve to twenty eggs, rather smaller than those of the goose, which are white, mixed with reddish or yellow freckles. They are very good in pastry, and mixed with fowls' eggs they improve omelets.

The question whether fowls or ducks are the better investment for the production of eggs has to some extent been settled experimentally in Germany and France in favor of ducks. They laid more eggs than the fowls, and, though they were rather smaller, they proved to be decidedly superior in nutritive material. It may be doubted whether as much attention is paid in England to the production of eggs as the utility of the food demands, and particularly by the poor, to whom their value is a consideration. Efforts should be made to induce all persons conveniently circumstanced to keep hens and ducks, and there is reason to believe that ducks are more profitable than hens, having regard to the number and size of the eggs laid by them. The solid matter and the oil in a duck's egg exceeds that of a hen's egg by as much as one fourth.

Eggs, their dietetic use apart, are of great utility in many branches of industry. In some, as in confectionery, both the whites and yolks are used, but usually the two find separate applications. The whites are employed in calico-printing, in photography, in gilding, in clarifying wines and liquors, and by the bookbinder on the leather previous to lettering or tooling.

An egg-oil is obtained in Russia in large quantities and of various qualities; the best so fine as to far excel olive-oil for cooking purposes. The less pure and very yellow qualities are chiefly used in the manufacture of the celebrated Kazan soap. Both of these products were shown at the London International Exhibition in 1862, and at subsequent exhibitions. Neither the oil for cooking purposes nor the soap are sufficiently cheap for general use; they are consumed only by the wealthy classes as luxuries; the soap, being regarded chiefly in the light of a cosmetic, is a much-valued addition to a Russian lady's toilet necessaries. The yolk is also used for medicinal purposes. It was used in the middle ages for the painter's art, before the discovery of oil-colors, as in the chapter-house at Westminster.

Eggs, whether to be used in culinary or pharmaceutical preparations, should be fresh. To determine this they should be examined by the light of a lamp. Fresh eggs are easily known by their transparency when held up to the light. By keeping they become cloudy, and when decidedly stale a distinct, dark, cloudlike appearance is discernible opposite some portion of the shell. Another simple mode is by placing the egg against the closed eyelid, and if the end of the egg is void it will feel warm, whereas if the egg is new laid it continues cold. A way to tell bad eggs is to put them in a pail of water, and, if good, they will lie on their sides; if bad, they will stand on their small ends, the large end always uppermost, unless they have been shaken considerably, when they will stand either end up.

How to keep eggs is a problem that has attracted the attention of inquirers from the earliest times. Twenty or more processes are generally known, all of which give unsatisfactory and incomplete results—a circumstance scarcely to be wondered at when the composition of an egg and the various changes to which it is subjected by exposure to atmospheric influence are taken into consideration. The egg-shell is furnished with numerous pores, through which the water evaporates, the loss of aqueous contents thus sustained being scarcely perceptible in the first week, more marked in the second, and of considerable interest in the third. The surrounding atmospheric air takes the place of the water that has evaporated, and oxygenates the contents of the shell, which then commence to ferment and are speedily spoiled. To hinder this evaporation, and so aid the preservation of eggs, they are often steeped for twelve hours in lime-water, by which means molecules of lime are deposited on the shell, and so obstruct the pores to some extent.

To the solution of the problem of how to prevent the air from penetrating the shell of the egg, the experiments of such eminent savants as Musschenbroek, Réaumur, and Nollet have greatly contributed. They all agree that the most practicable method is to envelop the new-laid egg in a light coating of some impermeable substance, such as wax, tallow, oil, or a mixture of wax and olive-oil, or of olive-oil and tallow. Réaumur suggested an alcoholic solution of resin, or a thick solution of gelatin. Nollet experimented successfully with India-rubber, collodion, and various kinds of varnish. At the Dairy Products Show at the Agricultural Hall in 1884, three prizes were awarded for eggs preserved in the following manner:

1. Eggs which had been dipped twice in a solution of gum arable and then dried, enveloped in paper, and kept in bran.

2. Eggs which had been rubbed with lard and then kept in dry salt.

3. Eggs coated with a composition of mutton and beef suet, and then wiped with a dry cloth.

With a view to utilizing in a more portable and consequently cheaper form the large supply of eggs obtainable in Austria, Messrs. Effner & Co. started a factory at Passau, in Bavaria, for condensing them. The eggs are carefully selected and dried, then reduced to a fine meal, and packed in tins ready for use. Although it is scarcely probable that the condensed egg can ever replace new-laid eggs for breakfast, it is asserted that a good omelet, as also the finest pastry, may be prepared from the product.

The eggs of wild birds are not very generally eaten in this country, but in some localities those of sea-fowl are largely consumed, and a considerable trade is carried on in gulls' eggs on many of our coasts. There is a great demand for plovers' eggs in the city markets for epicures. They are the eggs of the lapwing (Vanellus cristatus), a bird which lays about four eggs of an olive cast, spotted with black. These eggs come chiefly from Holland, the home produce being now very small, and they are received during the spring and summer, from March to June. Mr. Yarrell, who wrote many years ago, mentions that two hundred dozens of peewits' eggs were sent in one season from Romney Marsh to London. The eggs of many other species of birds are imposed upon the Londoners in the place of plovers' eggs.

In the sea islands of Alaska, the eggs of the thick-billed guillemot have an economic value, being the most palatable of all the varieties found in the islands, and hence are much sought after by the natives. The bird lays a single egg, large and very fancifully colored. The shell is so tough that, in gathering them, they are thrown into tubs and baskets on the cliffs, and poured out upon the rocks with a single flap of the hand, just as a sack of potatoes would be emptied, and only a trifling loss is sustained from broken or crushed eggs.

On the Faro Islands the number of eggs laid by the lesser black-backed gull, and sent annually to shore for culinary purposes, must be prodigious. The eggs of the common guillemot lie there so close together that it is difficult to move among them.

The eggs of the stork are very good eating, whether hot or cold. The natural color of the cormorant's egg seems to be a bluish green, like the usual variety of the common domestic duck, but over this is a thick, white, irregular covering of lime, which is frequently in such abundant quantity as to stand out in lumps on the surface, seldom allowing much of the original color to be visible. No doubt this superabundance of lime is produced by the bones of the fish, of which this bird is said to eat prodigious quantities, and perhaps also from shell-fish.

Turtles' eggs are held in great esteem wherever they are found, as well by Europeans as by others. They have a very soft shell, and are about the size of a pigeon's egg. The mother turtles lay three or four times a year, at intervals of two or three weeks. An experienced eye and hand are required to detect the eggs, as they are always ingeniously covered up with sand. The Orinoco and Amazon Indians obtain from these eggs a kind of clear, sweet oil, which they use instead of butter. In the month of February, when the high waters of the Orinoco have receded, millions of turtles come on shore to deposit their eggs. The certainty and abundance of the harvest is estimated by the acre. The yearly gathering about the mouth of the river Amazon alone is some five thousand jars of oil, and it takes five thousand eggs to make a jar. The turtle comes at night, and deposits from one hundred and forty to two hundred white eggs in the sand, carefully covering them up before returning to the sea. In about fourteen days she returns again to the same place to lay, and will come up about four times before stopping laying, thus giving some six hundred to eight hundred eggs. A native of Brazil will consume as many as twenty or thirty turtles' eggs at a meal, and a European will eat a dozen at a breakfast. They make an excellent omelet. The Indians frequently eat them raw, mixed with their cassava flour. The condition in which the egg of the turtle is best fit to be eaten is when taken from the slain animal, before the formation of the glaze and the surrounding parchment-like skin, which answers the purpose of a shell.

The eggs of a large lizard (Varanus vivitattus) are eaten in Java. In the West Indies the eggs of the iguana are thought a delicacy. One of these lizards will sometimes contain as many as fourscore eggs, which, when boiled, are like marrow. They are about the size of a pigeon's egg, but with a soft shell. The eggs of the common teguexin (Teius teguexin), and of other large species of lizards, are eaten in South America.

In the Antilles and on the west coast of Africa the eggs of the alligator are eaten. They resemble in shape a hen's egg, and have much the same taste, but are larger. More than a hundred eggs have been found in one alligator.

The large eggs of the boa constrictor are regarded as a dainty by the Africans from the Congo. One of these snakes, killed on an estate in British Guiana in 1884, had fifty eggs, which were eaten by the negroes.

The eggs of various fishes differ remarkably in external appearance. Some would scarcely be believed to be eggs at all. Take, for instance, the skate's egg. It looks like a flattened leather purse, with four horns or handles at the corners. The yolk is in the shape of a walnut, larger or smaller according to the species. In the Elasmobranchii, sharks and rays, the ova are not so numerous as those of other fishes, the eggs being generally inclosed in coriaceous or leathery capsules, familiarly known to sea-side visitors as mermaids' purses and the like.

The egg of the picked dog-fish, the yolk of which is about the size of a pigeon's egg, is used by the inhabitants in parts of Sweden and Norway as a substitute for other eggs in their domestic economy. Cod-roe is sold in London in a dried form, smoked, and thus darkly colored. It is a delicious dish when partly salted, parboiled, and then fried. Cod-roes are exported in tins to Australia and India in the salted state. The late Frank Buckland examined a cod-roe weighing seven pounds and three quarters, and found the average was one hundred and forty eggs to the grain. This gives 67,200 eggs to the ounce, so that in the whole mass of this one cod-roe, allowing three quarters of a pound for skin, membrane, etc., there were no less than 7,536,400 eggs.

Caviare is the common name for a preparation of the dried spawn or salted roe of fish. The black caviare is made from the roe of sturgeon, and a single large fish will sometimes yield as much as one hundred and twenty pounds of roe. A cheaper and less prized red kind is obtained from the roe of the gray mullet, and some of the carp species, which are common in the rivers and on the shores of the Black Sea. It is of interest to Turkey and the Levant trade only.

Botargo is a preparation made on the coasts of the Mediterranean, of the ovaries full of the mature eggs of the mullet (Mugil cephalus). The eggs are salted, crushed, reduced to a paste, and then dried in the sun. Sometimes spices or other ingredients are added. Botargo is eaten like caviare.

There is also a destruction by mankind of the ova or spawn of the Crustacea—lobsters, crabs, and shrimps—which are carried under their tail. The lobster produces from 25,000 to 40,000 eggs, the crayfish upward of 100,000. As much as six ounces of eggs can be taken off in May from a lobster weighing three to three pounds and a half, and there are about 6,720 eggs in an ounce of lobster spawn. The lobster is never so good as when in the condition of a "berried hen."

The eggs of some insects are eaten in Siam, Egypt, and Mexico, but those most valuable commercially are the eggs of the silk moth.

The trade in silk-worms' eggs from Japan has become an extensive and profitable one. In 1868 £1,000,000 was paid to Japan by the "graineurs" of Europe for silk-worms' eggs. In 1869 two million cards, costing on an average 12s. 6d. each, were sent to Europe. In other years three millions of these cards, packed in cases of about three hundred, thickly studded with these tiny specks, have been shipped from Japan by the various steamers.

In China and Japan the moths are placed to lay their eggs on cardboard or thick paper, which they cover regularly and closely with a secretion which glues them to the spot and acts as a preservative from heat or other accidents. Hence the cards may be transported many thousands of miles safely, in a ship with a properly regulated temperature, so as to prevent their hatching too soon. They should be arranged, and the cards thickly covered, without being overlaid, and having no unpleasant smell. A first glance at one of these cards would lead one to suppose that the eggs were artificially attached to the card, but the regularity is obtained by careful management of the moths at the time of laying the eggs. A vigorous moth will usually lay four or five hundred eggs. When the laying is terminated the peasants examine the cards, and, if there are any vacant places, attach a moth, by pins through its wings, so that the eggs may be deposited in the right place.—Abridged from the Journal of the Society of Arts.

  1. "Traité Général d'Oologie Ornithologique," par P. O. des Murs.