The Works of William Harvey M.D. / Translated from the Latin with a life of the author

by William Harvey

The proportion of the body to the extremities in children after their birth continues excessive until they begin to stand and run. Infants, therefore, resemble dwarfs in the beginning, and they creep about like quadrupeds, attempting progressive motion with the assistance of all their extremities; but they cannot stand erect until the length of the leg and thigh together exceeds the length of the rest of the body. And so it happens, that when they first attempt to walk, they move with the body prone, like the quadruped, and can scarcely rise so erect as the common dunghill fowl.

And so it happens that among adult men the long-legged—they who have longer legs, and especially longer thighs—are better walkers, runners, and leapers than square-built, compact men.

In this second process many actions of the formative faculty are observed following each other in regular order, (in the same way as we see one wheel moving another in automata, and other pieces of mechanism,) and all arising from the same mucaginous and similar matter. Not indeed in the manner that some natural philosophers would have it when they say, “that like is carried to its like.” We are rather to maintain that parts are moved, not changing their places, but remaining and undergoing change in hardness, softness, colour, &c., whence the diversities between similar parts; those things appearing in act which were before in power.[297] The extremities, spine, and rest of the body, namely, are formed, grow, and acquire outline and complexion together; the extremities, comprising bones, muscles, tendons, and cartilages, all of which on their first appearance were similar and homogeneous, become distinguished in their progress, and, connected together, compose organs, by whose mutual continuity the whole body is constituted. In like manner, the membrane growing around the head, the brain is composed, and the lustrous eyes receive their polish out of a perfectly limpid fluid.

That is to say, nature sustains and augments the several parts by the same nourishment with which she fashioned them at first, and not, as many opine, with any diversity of aliment and particles similar to each particular structure. As she is increasing the mucaginous mass or maggot, like a potter she first divides her material, and then indicates the head and trunk and extremities; like a painter, she first sketches the parts in outline, and then fills them in with colours; or like the shipbuilder, who first lays down his keel by way of foundation, and upon this raises the ribs and roof or deck: even as he builds his vessel does nature fashion the trunk of the body and add the extremities. And in this work she orders all the variety of similar parts—the bones, cartilages, membranes, muscles, tendons, nerves, &c.—from the same primary jelly or mucus. For thick filaments are produced in the first instance, and these by and by are brought to resemble cords; then they are rendered cartilaginous and spinous; and, lastly, they are hardened and concocted into bones. In the same way the thicker membrane which invests the brain is first cartilaginous and then bony, whilst the thinner membrane merely consolidates into the pericranium and integument. In similar order flesh and nerve from soft mucus are confirmed into muscle, tendon, and ligament; the brain and cerebellum are condensed out of a perfectly limpid water into a firm coagulum; for the brain of infants, before the bones of the head have closed, is soft and diffluent, and has no greater consistence than the curd of milk.

The third process is that of the viscera, the formation of which in the chick takes place after the trunk is cast in outline, or about the sixth or seventh day,—the liver, lungs, kidneys, cone and ventricles of the heart, and intestines, all become visible nearly at the same moment; they appear to arise from the veins, and to be connected with them in the same way as fungi grow upon the bark of trees. They are, as I have already said, gelatinous, white, and bloodless, until they take on their proper functions. The stomach and intestines are first discovered as white and tortuous filaments extending lengthwise through the abdomen; along with these the mouth appears, from which a continuous canal extends to the anus, and connects the superior with the inferior parts. The organs of generation likewise appear about the same time.

Up to this period all the viscera, the intestines, and the heart itself inclusive, are excluded from the cavities of the body and hang pendulous without, attached as it were to the veins. The trunk of the body presents itself, in fact, like a boat undecked or a house without a roof, the anterior walls of the thorax and abdomen not being yet extant to close these cavities.

But as soon as the sternum is fashioned the heart enters into the chest as into a dwelling which it had built and arranged for itself; and there, like the tutelary genius, it enters on the government of the surrounding mansion, which it inhabits with its ministering servants the lungs. The liver and stomach are by and by included within the hypochondria, and the intestines are finally surrounded by the abdominal parietes. And this is the reason wherefore without dissection the heart can no longer be seen pulsating in the hen’s egg after the tenth day of incubation.

About this epoch the point of the beak and the nails appear of a fine white colour; a quantity of chylous matter presents itself in the stomach; a little excrement is also observed in the intestine, and the liver being now begun, some greenish bile is perceived; facts from which it clearly appears that there is another digestion and preparation of nutriment going on besides that which takes place by the branches of the umbilical veins; and it is reasonable matter of doubt how the bile, the excrementitious matter of the second digestion, can be separated by the instrumentality of the liver from the other humours, when we see it produced at the same time as this organ.

In the order now indicated are the internal organs generated universally; in all the animals which I have dissected, particularly the more perfect ones, and man himself, I have found them produced in the same manner: in these, in the course of the second, third, and fourth month, the heart, liver, lungs, kidneys, spleen, and intestines present themselves inchoate and increasing, and all alike of the same white colour which belongs to the body at large. Wherefore these early days are not improperly spoken of as the days when the embryo is in the milk; for with the exception of the veins, particularly those of the umbilicus, everything is as it were spermatic in appearance.

I am of opinion that the umbilical arteries arise after the veins of the same name, because the arteries are scarcely to be discovered in the course of the first month, and take their rise from the branches that descend to either lower extremity. I do not believe, therefore, that they exist until that part of the body whence they proceed is formed. The umbilical veins, on the contrary, are conspicuous long before any part of the body is begun.