1846 The Lancet  
IT has been already stated that the blood of the fcotal chick, which circulates in the membranes, runs towards the narrow end of the egg, and returns from the broad end to the chick. This peculiar course never varies, whether the chick be a male or a female, and in whatever position it may be placed. This circumstance indicates that the course of these vessels proceeds, not from any provision inherent in the primordium, but in the egg itself. What, then, is the cause of this particular
more » ... particular arrangement of these vessels ? We know that the egg is composed of parts peculiarly arranged and held together by a particular kind and amount of force, and that so long as this kind and amount of force exist, the egg continues in a state of integrity. We likewise know that the folliculus aeris is almost invariably situated at the broad end of the egg, and that this cavity progressively enlarges as the egg increases in age. We further know that the foetal chick progressively approaches the folliculus aeris, that the glaire or albumen is progressively drawn towards, and taken from, the narrow end of the egg, and is the pristine and most important food of the foetus. These circumstances indicate that the narrow end of the egg inherits a power which does not exist in its broad end, and that this power has an attractive influence; and hence that there exists in the egg either a polarity, or something of a polar nature, and that this polar influence is the probable cause of the peculiar arrangement of the bloodvessels, which ramify in the membranes of the primordium. . On the fifth day of hatching, the various structures of the chick already noticed are more fully developed. The rudiments of the toes are now recognised. At this period, the heart retains its actions for a longer period, when cold water i,4 applied to the outer surface of the egg-shell, than on the preceding day, and these actions, when rendered quiescent by cold, can be reproduced by heat with greater facility. At this period of hatching, the folliculus aeris is much enlarged, the yelk has a muddy appearance, and the colour of whey; the albumen lies under the yelk, and is so thick and tenacious as to appear like a firm jelly. The chick is fixed to the yelk and respiratory membrane by bloodvessels, and the respiratory membrane slides over the inner surface of the chorion, and hence enables the chick to lie uppermost in every position of the egg. The surface of the membrana vitelli, which lies uppermost, is not so vascular or so thick as its other parts, but the inner surface has throughout a beautiful reticulated appearance. At this period of hatching, the auricles of the heart of the chick are not serrated at their margins, and the heart has the shape represented in figure 19 . On the sixth day of hatching, the chick is, with the exception of the abdominal opening, fully developed, and moves the several parts of its body, and the coccyx in particular, very frequently. The body lies nearer the folliculus aeris, and the albumen or glaire of the egg has a less muddy appearance. At this period of life, reiterated experiments prove that when the actions of the heart cease to exist by cold, they can be reproduced by heat at 104° Fahrenheit, and that these reproduced actions are not so readily evolved, nor so long in duration, as on the preceding inquiries. On the seventh day of hatching, the chick is much larger than on the preceding day. The walls of the thorax are now so thick and opaque, as to prevent the actions of the heart from being readily seen. The eyes are now completely formed. The chick lies nearer the broad end of the egg, and is progressively approaching the folliculus aeris. On the eighth day of hatching, the chick is about one inch in length, from the head to the tail, and lies under the folli. culus aeris. It has still an opening into the abdomen. The bloodvessel which passes from the chick towards the broad, and runs in the respiratory membrane towards the narrow end of the egg, contains blood of a bright scarlet colour; and the other bloodvessel, which runs from the chick in a contrary direction, contains blood of a dark vermillion hue, and pulsates. These circumstances are better recognised at this than at any former period of life. The albumen of the egg is again perfectly transparent, and is much diminished in quantity. It is now placed at the narrow end of the egg, a very small portion of it being in contact with the chick. ' On the ninth day of hatching, the chick is more perfect in its several structures; a white limey spot is now seen at the point of its beak. On the tenth day of hatching, the chick lies close under the folliculus aeris, at the broad end of the egg, and moves its head, wings, legs, in fact, its whole body, with facility; and from these motions the liquor amnii has an undulating motion similar to the ebbing and flowing of the tide, and to respiration. The cutis anserinus of the chick is now completely developed. The albumen of the egg is now much less in quantity, has a pure amber colour, is more glutinous than in a new laid egg, and is placed at the narrow end of the egg. It seems to adhere to the membrana vitelli, and where it is adherent, the membrane has a lighter colour, and appears less vascular than at any other part; and between these parts, a dark-coloured and vascular portion of membrana vitelli, like a belt, is seen. The yelk of the egg does not, as yet, seem to have decreased in magnitude, and become less in quantity. Figure 20 represents the relative positions of the parts now noticed. FiG. 20. 1, Folliculus aeris. 2, Chick. 3, Yelk. 4, Belt. 5, Albumen. On the eleventh day of hatching, the chick is about two inches in length, and has a ridge formed by the roots of feathers, extending from the crown of the head, along the spine to the coccyx. The chick now opens and shuts its beak very frequently. Reiterated experiments prove that the actions of the heart are as much influenced by heat and cold as at any former period of life. At this period of life, I accidentally noticed that the body moved as if the animal breathed. This respiratory action is perhaps the motion recognised at the twentyseventh hour of hatching. It is similar to the motion noticed in the gills of fish, and in the nymphae of the dragon-fly. On the twelfth day of hatching, the skin of the chick is covered with the roots of feathers, and surrounded with liquor amnii, which is clear and colourless. The yelk of the egg is not apparently the least diminished in magnitude, but is very soft to the touch, and is somewhat of a fluid consistence. , On the thirteenth day of hatching, the chick is thickly covered with feathers. The albumen of the egg is now about the size of two kidney-beans, and is quite transparent. The yelk, when its membrane has a whiter colour than its other parts, has a wheyish colour. Several white, flaky substances, of an earthy or limey nature, are now seen lying in the folds of the membranes. These white substances increase progressively in size and number, and become more consistent as the chick advances in age. But more of this hereafter. On the fourteenth day of hatching, the chick lies embedded, as it were, in the yelk, which has not, as yet, diminished much in magnitude. The albumen, on the contrary, is small in quantity. The amniotic fluid is likewise much diminished in quantity, and, when mixed with cold water, it makes the water muddy. The blastoderma is now the largest membrane
doi:10.1016/s0140-6736(02)35056-6 fatcat:w2j35cr4ifbghfpyb2d23tmhwq