Our Humble Helpers: Familiar Talks on the Domestic Animals

by Jean-Henri Fabre

“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 [[38]]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 [[39]]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.” [[40]]

“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 chalazæ. 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 chalazæ. 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 rôle—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 [[41]]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 [[42]]your small powers of comprehension, I abridge, much to my regret.