The Egg Continued
( Originally Published 1918 )
"LET us return to the hen. We know the calcareous nature of the shell; now let us look at the structure. Open your eyes wide and look attentively; you will see on the shell, chiefly at the large end, a multitude of tiny dents such as might be made by the point of a fine needle. Each of these dents corresponds to an invisible hole that pierces the shell through and through and establishes communication between the interior and the exterior. These holes, much too small to let out the liquid contents of the egg, nevertheless suffice both for the emission of humid vapors, which are dissipated outside the shell, and for the admission of air, which penetrates within and replaces the evaporated humidity.
"The presence of these innumerable openings is absolutely necessary for the awakening and keeping up of life in the future chicken. Every living thing breathes, and all life springs into being and continues through the action of air. The seed that germinates under ground must have air. Planted too deep, it perishes sooner or later without being able to rise, because the thick bed of earth prevents the air from reaching it. The egg must have air so that its substance, gently warmed by the brooding mother hen, may spring into life and become a little chicken; it must have it continually, shut up as it is in its shell. Thanks to the openings with which the shell is riddled, the air penetrates sufficiently to meet the needs of respiration ; it quickens the substance of the egg and the little being slowly forming within."
"One might say," Emile here put in, "that these holes are so many little windows through which air reaches the bird in its narrow cell of the egg."
"These windows, as Emile calls them," his uncle went on, "deserve our attention from another point of view. Eggs are a precious alimentary provision; the difficulty is to keep them for any length of time. If they get too old they spoil and give out then an infectious, bad smell. Well, then, what causes the eggs to spoil and changes them to repulsive-smelling filth is again air—the same air so indispensable to the formation of the chicken. That which gives life to the egg under the heat of the brooding hen brings destruction just as quickly when the warmth is wanting. If, then, it is proposed to preserve in a state of freshness as long as possible eggs destined for food, it is necessary to prevent the access of air into their interior, which is done by closing the openings in the shell. Several means may be employed. Sometimes eggs are plunged for a moment into melted grease, from which they are drawn out covered with a coating that obstructs all the orifices ; sometimes they are varnished. The simplest method is to keep them in water in which a little lime has been dissolved. This dissolved lime deposits itself on the shell and closes the openings. These pre-cautions taken, the air can no longer find a passage to penetrate into the interior and the eggs are preserved in good condition much longer than they would be without this preparation. Nevertheless they always spoil in the long run."
If I have properly understood what you have just told us about the need of air for the awakening of life," remarked Jules, "eggs thus coated with varnish or lime will not hatch when under the brooding hen?"
"Evidently not. Rendered impervious to air by the varnish, lime, grease, or what not, the eggs might remain indefinitely under the brooding hen without ever coming to life; for want of the quickening action of the air, life would no more awaken in them than in simple stones. You understand, then, that the method of preservation by means of a coating that closes the orifices of the shell must only be employed for eggs destined for food, and that care must be taken not to make use of it in those destined for hatching.
"But this is enough about the outside of the egg. Now let us break the shell. What do we find within? We find a delicate membrane, a supple skin which lines the whole of the shell and forms a kind of bag, without any opening, filled with the white and yolk. When by some accident the limy coating is lacking, this membrane constitutes the sole covering of the egg—a covering as soft as thin parchment soaked in water."
"Then soft eggs without any shell have this membrane all exposed?" queried Jules.
"Exactly. A new-laid egg has its shell completely filled; but it soon loses some of its humidity, which evaporates through the orifices in the shell. A void is then created in the interior, near the large end, where the evaporation is most rapid. At this end, therefore, the membrane detaches itself from the shell that it lined and draws further in with the contents of the egg shrunk by the evaporation. Thus is produced at the large end a cavity which the air from outside enters and which for this reason is called the air-chamber. This chamber, wanting at first, grows little by little according to the space left by the moisture's evaporation; consequently, the older the egg, the larger the space. If the egg is placed under the hen, the heat of the mother aids evaporation and causes the quick formation of the air-chamber. There gathers, as in a reservoir, the supply of air needed for the vitality of the egg and the respiration of the coming bird. So the empty space at the large end is a respiratory storehouse.
"When you eat an egg boiled in the shell, break it carefully at the large end. If the egg is very fresh the white will be seen immediately under the shell without any empty space; but if it is old you will find an unoccupied hollow of varying size. That is the air-chamber. According to its size you can judge of the egg's freshness. But it would be more desirable to be able to recognize, before using and breaking it, whether an egg is fresh or stale. I have seen the following means used, which would seem very strange if what I have just told you about the air-chamber did not furnish the explanation. The tip of the tongue is applied to the large end. If the egg is fresh a slight impression of coolness can be felt; if stale, the tongue remains warm. This little mystery is based on the different manner of behavior of liquids and gases when brought into contact with heat. Water and liquids in general take away rather quickly the heat of the bodies with which they come in contact; air and other gases, on the contrary, take it away very slowly. That is why water seems cold when we plunge our hand into it, while the air, lower in temperature, seems warm by comparison. In reality, if both be of the same temperature, air and water give us different sensations: water is cool to us because it draws our heat away; air warm because it does not take away that same heat. So if the egg is fresh, and consequently the shell completely filled, the tip of the tongue applied to the large end feels the same sensation as comes from contact with liquids; that is to say, a feeling of coolness. But if the egg is stale, an air-chamber has formed and the resulting sensation is that produced by contact with a gas ; that is to say, a 'sensation of warmth, since the tongue loses none of its natural heat."
"That is certainly a curious test," said Jules, "and I shall make it a point to carry it out at the next opportunity."
"Let us go on with the egg. Now comes the glair or white, so called because heat hardens it to a pure white matter. For the same reason, science calls it albumen, from a Latin word, albus, meaning white. The glair is arranged in a number of layers, which at both ends of the egg twist round one another and form two large knotty cords called chalazce. To see these cords you must break a raw egg carefully in a plate. Then you can distinguish, on each side of the yolk, a mass where the glair is thicker and rather knotty. There, somewhat injured by the breaking of the egg, are found the two cords in question. To give you a clear idea, take an orange, put it in your handkerchief, and twist the latter in opposite directions at both ends. The orange in its handkerchief covering will represent the spherical yolk surrounded by the glair; the two twisted ends of the handkerchief will be the two strings of white, the two chalazae. By means of these two tethers the yolk, the most important and most delicate part of the egg, is suspended as in a hammock, in the center of the glair, without being exposed to disturbances that would be dangerous for the germ of life situated at a point on its surface. This glairy hammock, with its two suspending cords, has another role—a very delicate one. The first outlines of the coming chick will appear at a certain point of the yolk. As the little being forms and grows, it needs more space while still remaining tightly enveloped and held in position so as to avoid the slightest disturbance in the half fluid flesh just beginning to assume its proper shape. How are these conditions realized in the egg? To understand the matter thoroughly let us go back to the orange wrapped in a handkerchief twisted at both ends. Is it not true that if both ends untwist a little, the orange, supposing it to need by degrees more room, will always find the necessary space without for a moment ceasing to be enveloped and motionless? In the same manner the suspending cords of the white slacken and gradually untwist as the little bird grows, at the expense of the yolk, in its soft hammock of glair; the needed space is made, and at the same time the feeble little bird remains just as finely swaddled and suspended in the center of the egg, protected from contact with the hard shell."
"At the beginning," interposed Jules, "you called an egg a marvel. I see that there are, in fact, in the egg things very worthy of our admiration : the shell, with its numerous air-holes; the cavity at the large end; the air-chamber where provision is made for breathing; the soft little bed of glair with its suspending cords that untwist to make more room, and perhaps that is not all?"
"No, my friend, that is very far from being all. I limit myself here to the simplest things and those that are not beyond your grasp. How would it be if you could follow me in the unfolding of higher ideas? You would see how everything in the egg is arranged with infinite delicacy, with a foresight that we may call maternal, and then you would find my word marvel the right one. But, not to go beyond your small powers of comprehension, I abridge, much to my regret.
"The yolk or yelk (which means the yellow part) is round and bright yellow; hence its name. At a point on its surface, generally at the top, no matter what the position of the egg, is seen a circular spot, dull white, where the matter is a little more condensed than elsewhere. It is called the cicatricle, or little scar. That is the sacred spot where lies the spark of life which, animated by incubation, will quicken the substance of the egg and mold it into a living being; it is the point of departure, the origin, the germ of the bird. The yolk itself is the nutritive reservoir whence are drawn the materials for this work of creation. Quickened by the heat of the brooding hen and by the action of the air, it becomes covered with a network of fine veins. These swell with the substance of the yolk, which turns to blood; and this blood, carried hither and thither, becomes the flesh of the being in process of formation. The yolk, then, is the bird's first food, but food that no beak seizes and no stomach digests, none being in existence yet. It changes to blood and afterward to flesh without the preparatory work of ordinary digestion; it enters the veins directly, and thus nourishes the whole body.
`Animals with udders—the mammifers—also have nutriment for the very young in the form of milk, which is indispensable for the weak stomach of the nursling. Well, the yolk is to the bird in its shell what milk is to the lamb and kitten; it is its milk-food, as it can have no recourse to maternal udders. The popular saying has perfectly caught the strict resemblance : they call a drink prepared with the yolk of an egg, 'hen's milk.' "
"That is what Mother Ambroisine makes me take when I cough in the winter," said Emile.
"The delicious beverage that Mother Ambroisine gives you when you have a cold is very properly called 'hen's milk,' since it is made with the equivalent of milk; that is to say, the yolk of an egg."