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

by William Harvey

The egg in the same way is fruitful which differs from a subventaneous or hypenemic egg, and which, cherished by incubation, or in any other way, does not fail to produce a chick.

Such an efficient cause consequently is required for the chick, as shall impart the virtue of fecundity to it, and secure it the power of acting as an efficient cause in its turn. Because that, or its analogue at least, by means of which they become prolific, is present in all animals. And the inquiry is the same in each case, when we ask what it is in the egg which renders it prolific, and distinguishes it from a wind egg; what in the vitellary germ and ovary; what in the female; what, finally, in the semen and the cock himself? What, moreover, it is in the blood and punctum saliens, or first formed particle of the chick, whence all the other parts arise with their appropriate structures and arrangements; what in the embryo or chick itself whereby it becomes more or less robust and agile, attains to maturity with greater or less rapidity, and lives with various degrees of health, for a longer or shorter period?

Nor is the inquiry very different which goes to ascertain what sex the male and the female, or the cock and the hen, confer upon the prolific egg; and what proceeds from each that contributes to the perfection or resemblance of the chick, viz., whether the egg, the conception, the matter, and the nutriment proceed from the mother, and the plastic virtue from the father; or rather a certain contagion immitted during intercourse, or produced and received from him, which in the body of the hen, or in the eggs, either permanently excites the matter of the eggs, or attracts nourishment from the female, and concocts and distributes it first for the growth of the eggs, and then for the production of the chicks; finally, whether from the male proceeds all that has reference to form and life and fecundity, from the female, again, all that is of matter, constitution, place, and nourishment? For among animals where the sexes are distinct, matters are so arranged, that since the female alone is inadequate to engender an embryo and to nourish and protect the young, a male is associated with her by nature, as the superior and more worthy progenitor, as the consort of her labour, and the means of supplying her deficiencies; in the case of the hen, of correcting by his contagion the inferiority of the hypenemic eggs which she produces, and so rendering them prolific. For as the pullet, engendered of an egg, is indebted to that egg for his body, vitality, and principal or generative part, so and in like manner does the egg receive all that is in it from the female, the female in her turn being dependent on the male for her fecundity which is conferred in coition.

And here we have an opportunity of inquiring, whether the male be the first and principal cause of the generation of the offspring; or whether the male along with the female are the mediate and instrumental causes of nature itself, or of the first and supreme generator? And such an inquiry is both becoming and necessary, for perfect science of every kind depends on a knowledge of causes. To the full understanding of generation, therefore, it is incumbent on us to mount from the final to the first and supreme efficient cause, and to hold each and every cause in especial regard.

We shall have occasion to define that which is the first and supreme efficient cause of the chick in ovo by and by, when we treat of that which constitutes the efficient cause [of generation] among animals in general. Here, meantime, we shall see what its nature may be.

The first condition, then, of the primary efficient cause of generation, properly so called, is, as we have said, that it be the prime and principal fertilizer, whence all mediate causes receive the fecundity imparted. For example, the chick is derived from the punctum saliens in the egg, not only as regards the body, but also, and this especially, as respects the life (anima): the punctum saliens, or heart, is derived from the egg, the egg from the hen, and the hen has her fecundity from the cock.

Another condition of the prime efficient is discovered from the work achieved, viz., the chick, because that is the prime efficient in which the reason of the effect is principally displayed. But since every generative efficient engenders another like itself, and the offspring is of a mixed nature, the prime efficient must also be a certain mixed something.

Now, I maintain that the offspring is of a mixed nature, inasmuch as a mixture of both parents appears plainly in it, in the form and lineaments, and each particular part of its body, in its colour, mother-marks, disposition to diseases, and other accidents. In mental constitution, also, and its manifestations, such as manners, docility, voice, and gait, a similar temperament is discoverable. For as we say of a certain mixture, that it is composed of elements, because their qualities or virtues, such as heat, cold, dryness, and moisture, are there discovered associated in a certain similar compound body, so, in like manner, the work of the father and mother is to be discerned both in the body and mental character of the offspring, and in all else that follows or accompanies temperament. In the mule, for instance, the body and disposition, the temper and voice, of both parents (of the horse and the ass, e. g.) are mingled; and so, also, in the hybrid between the pheasant and the fowl, in that between the wolf and the dog, &c., corresponding traits are conspicuous.

When, therefore, the chick shows his resemblance to both parents, and is a mixed effect, the primary genital cause (which it resembles) must needs be mixed. Wherefore that which fashions the chick in the egg is of a mixed nature, a certain something mixed or compounded, and the work of both parents. And if any kind of contagion, engendered under the influence of sexual intercourse, in which the male and female mingle and form but one body, either originates or remains in the body of the female, that, too, must be of a mixed nature or power, whence, subsequently, a fertile egg will be produced, endowed with plastic powers, the consequence of a mixed nature, or of a mixed efficient instrument, from which a chick, also of a mixed nature, will be produced.

I have used the word contagion above, because Aristotle’s view is contradicted by all experience, viz., that a certain part of the embryo is immediately made by intercourse. Neither is it true, as some of the moderns assert, that the vital principle (anima) of the future chick is present in the egg; for that cannot be the vital principle of the chick which inheres in no part of its body. Neither can the living principle be said either to be left or to be originated by intercourse; otherwise in every pregnant woman there would be two vital principles (animæ) present. Wherefore, until it shall have been determined what the efficient cause of the egg is, what it is of mixed nature that must remain immediately upon intercourse, we may be permitted to speak of it under the title of a Contagion.