William Harvey

by Sir D'Arcy Power

Harvey’s powers of observation were particularly brought into play in connection with his experiments on the development of the chick. He fully appreciated the method of Zadig, for he says that “different hens lay eggs that differ much in respect of size and figure, some habitually lay more oblong, others rounder eggs that do not differ greatly from one another: and although I sometimes found diversities in the eggs of the same fowl, these were still so trifling in amount that they would have escaped any other than the practised eye ... so that I myself, without much experience, could readily tell which hen in a small flock had laid a given egg and that they who have given much attention to the point of course succeed much better. But that which we note every day among huntsmen is far more remarkable: for the more careful keepers who have large herds of stags or fallow deer under their charge, will very certainly tell to which herd the horns they find in the woods or thickets belonged. A stupid and uneducated shepherd, having the charge of a numerous flock of sheep, has been known to become so familiar with the physiognomy of each, that if any one had strayed from the flock though he could not count them, he could still say which one it was, give the particulars as to where it had been bought or whence it had come. The master of this man for the sake of trying him, once selected a particular lamb from among forty others in the same pen and desired him to carry it to the ewe which was its dam, which he did forthwith. We have known huntsmen who having only once seen a particular stag or his horns or even his print in the mud (as a lion is known by his claws) have afterwards been able to distinguish him by the same marks from every other. Some, too, from the footprints of deer, seen for the first time, will draw inferences as to the size and grease and power of the stag which has left them: saying whether he were full of strength or weary from having been hunted, and farther whether the prints are those of a buck or doe. I shall say this much more, there are some who in hunting, when there are some forty hounds upon the trace of the game and all are giving tongue together will nevertheless, and from a distance, tell which dog is at the head of the pack, which at the tail, which chases on the hot scent, which is running off at fault, whether the game is still running or at bay, whether the stag have run far or have but just been raised from his lair. And all this amid the din of dogs and men and horns and surrounded by an unknown and gloomy wood. We should not therefore be greatly surprised when we see those who have experience telling by what hen each particular egg in a number has been laid. I wish there was some equally ready way from the child of knowing the true father.”

The next extract gives a good example of Harvey’s general style. Speaking of the escape of the chicken from the egg, he says: “Now we must not overlook a mistake of Fabricius and almost every one else in regard to this exclusion or birth of the chick. Let us hear Fabricius.

“‘The chick wants air sooner than food, for it has still some store of nourishment within it: in which case the chick by his chirping gives a sign to his mother of the necessity of breaking the shell, which he himself cannot accomplish by reason of the hardness of the shell and the softness of his beak, to say nothing of the distance of the shell from the beak and of the position of the head under the wing. The chick, nevertheless, is already so strong, and the cavity in the egg is so ample, and the air contained within it so abundant, that the breathing becomes free and the creature can emit the sounds that are proper to it. These can be readily heard by a bystander, and were recognised both by Pliny and Aristotle, and perchance have something of the nature of a petition in their tone. For the hen hearing the chirping of the chick within, and knowing thereby the necessity of now breaking the shell in order that the chick may enjoy the air which has become needful to it, or if you will, you may say, that desiring to see her dear offspring, she breaks the shell with her beak, which is not hard to do, for the part over the hollow long deprived of moisture and exposed to the heat of incubation, has become dry and brittle. The chirping of the chick is consequently the first and principal indication of the creature desiring to make its escape and of its requiring air. This the hen perceives so nicely, that if she hears the chirping to be low and internal, she straightway turns the egg over with her feet, that she may break the shell at the place whence the voice proceeds without detriment to the chick.’ Hippocrates adds, ‘Another indication or reason of the chick’s desiring to escape from the shell, is that when it wants food it moves vigorously, in search of a larger supply, by which the membrane around it is torn, and the mother breaking the shell at the place where she hears the chick moving most lustily, permits it to escape.’

“All this is stated pleasantly and well by Fabricius; but there is nothing of solid reason in the tale. For I have found by experience that it is the chick himself and not the hen that breaks open the shell, and this fact is every way in conformity with reason. For how else should the eggs which are hatched in dung-hills and ovens, as in Egypt and other countries, be broken in due season, where there is no mother present to attend to the voice of the supplicating chick and to bring assistance to the petitioner? And how again are the eggs of sea and land tortoises, of fishes, silkworms, serpents, and even ostriches to be chipped? The embryos in these have either no voice with which they can notify their desire for deliverance, or the eggs are buried in the sand or slime where no chirping or noise could be heard. The chick, therefore, is born spontaneously, and makes its escape from the eggshell through its own efforts. That this is the case appears from unquestionable arguments: when the shell is first chipped the opening is much smaller than accords with the beak of the mother, but it corresponds exactly to the size of the bill of the chick, and you may always see the shell chipped at the same distance from the extremity of the egg and the broken pieces, especially those that yield to the first blows, projecting regularly outwards in the form of a circlet. But as any one on looking at a broken pane of glass can readily determine whether the force came from without or from within by the direction of the fragments that still adhere, so in the chipped egg it is easy to perceive, by the projection of the pieces around the entire circlet, that the breaking force comes from within. And I myself, and many others with me besides, hearing the chick scraping against the shell with its feet, have actually seen it perforate this part with its beak and extend the fracture in a circle like a coronet. I have further seen the chick raise up the top of the shell upon its head and remove it.

“We have gone at length into some of these matters, as thinking that they were not without all speculative interest, as we shall show by and by. The arguments of Fabricius are easily answered. For I admit that the chick produces sounds whilst it is still within the egg, and these perchance may even have something of the implorative in their nature: but it does not therefore follow that the shell is broken by the mother. Neither is the bill of the chick so soft, nor yet so far from the shell, that it cannot pierce through its prison walls, particularly when we see that the shell, for the reasons assigned, is extremely brittle. Neither does the chick always keep its head under its wing, so as to be thereby prevented from breaking the shell, but only when it sleeps or has died. For the creature wakes at intervals and scrapes, and kicks, and struggles, pressing against the shell, tearing the investing membranes and chirps (that this is done whilst petitioning for assistance I willingly concede), all of which things may readily be heard by any one who will use his ears. And the hen, listening attentively, when she hears the chirping deep within the egg, does not break the shell, but she turns the egg with her feet, and gives the chick within another and a more commodious position. But there is no occasion to suppose that the chick by his chirping informs his mother of the propriety of breaking the shell, or seeks deliverance from it; for very frequently for two days before the exclusion you may hear the chick chirping within the shell. Neither is the mother when she turns the egg looking for the proper place to break it; but as the child when uncomfortably laid in his cradle is restless and whimpers and cries, and his fond mother turns him this way and that, and rocks him till he is composed again, so does the hen when she hears the chick restless and chirping within the egg, and feels it, when hatched, moving uneasily about in the nest, immediately raise herself and observe that she is not pressing upon it with her weight, or keeping it too warm, or the like, and then with her bill and her feet she moves and turns the egg until the chick within is again at its ease and quiet.”

This extract shows that here, as in all Harvey’s work there was a union of common sense, observation, and experiment which enabled him to overturn without any unkindly feeling the cherished teachings of his predecessors and contemporaries.

When it was necessary he did not hesitate to experiment upon himself, for he says: “I have myself, for experiment’s sake, occasionally pricked my hand with a clean needle, and then having rubbed the same needle on the teeth of a spider, I have pricked my hand in another place. I could not by my simple sensation perceive any difference between the two punctures: nevertheless there was a capacity in the skin to distinguish the one from the other; for the part pricked by the envenomed needle immediately contracted into a tubercle, and by and by became red, hot, and inflamed, as if it collected and girded itself up for a contest with the poison for its overthrow.”

The seventy-first essay of the treatise of Development is a good example of the mystic or philosophical side of Harvey’s character. The essay is entitled “Of the innate Heat.” It begins, “As frequent mention is made in the preceding pages of the calidum innatum or innate heat, I have determined to say a few words here, by way of dessert, both on that subject and on the humidum primigenium or radical moisture, to which I am all the more inclined because I observe that many pride themselves upon the use of these terms without, as I apprehend, rightly understanding their meaning. There is, in fact, no occasion for searching after spirits foreign to or distinct from the blood; to evoke heat from another source; to bring gods upon the scene, and to encumber philosophy with any fanciful conceits. What we are wont to derive from the stars is in truth produced at home. The blood is the only calidum innatum or first engendered animal heat.”

Harvey then proceeds to examine the evidence for a spirit different from the innate heat, of celestial origin and nature, a body of perfect simplicity, most subtle, attenuated, mobile, rapid, lucid, ethereal, participant in the qualities of the quintessence. Of this spirit Harvey confesses that “we, for our own parts, who use our simple senses in studying natural things, have been unable anywhere to find anything of the sort. Neither are there any cavities for the production and preservation of such spirits, either in fact or presumed by their authors.”