Page:The Works of William Harvey (part 1 of 2).djvu/464

 power, whence, subsequently, a fertile egg will be produced, endowed with plastic powers, the consequence of a mixed na- ture, 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 princi- ple (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 (animae) present. Wherefore, until it shall have been deter- mined 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.

But where this contagion lies hid in the female after inter- course, and how it is communicated and given to the egg, de- mands quite a special inquiry, and we shall have occasion to treat of the matter when we come to discuss the conception of females in general. It will suffice, meantime, if we say that the same law applies to the prime efficient' in which inheres the reason of the future offspring as to the offspring ; as this is of a mixed nature, the nature of its cause must also be mixed; and it must either proceed equally from both parents, or from something else which is employed by both concurrently as in- struments, animated, co-operating, mixed, and in the sexual act coalescing unto one. And this is the third condition of the prime efficient, that it either imparts motion to all the in- termediate instruments in succession, or uses them in some other way, but comes not itself into play. Whence the origin of the doubt that has arisen, whether, in the generation of the chick, the cock were the true prime efficient, or whether there were not another prior, superior to him? For, indeed, all things seem to derive their origin from a celestial influence, and to follow the movements of the sun and moon. But we shall be able to speak more positively of this matter after we haye shown what we understand by the " instrument," or " in- strumental efficient cause," and how it is subdivided.