I] CHEMICAL EMBRYOLOGY ii 



further remark, gentle heat-in-general joined with the essence-of- 

 eggness would produce only hatching-as-such and not the hatching 

 of a chicken, so that a third influence, which they call the Final 

 Cause, or the End-in-view, must operate as well, and this guiding 

 influence is the divine idea of a perfect cock or a perfect hen presiding 

 over the incubation and causing the mere eggness in the egg to 

 assume the likeness of the animals from which it came. Nor, finally, 

 do they find that these three influences are sufficient to produce here 

 and now this particular chicken, but are compelled to add a fourth, 

 a Formal Cause, namely, a particular yolk, a particular shell, and 

 a particular farmyard, on which and in which the other three causes 

 may work, and laboriously hatch an individual chicken, probably 

 lame and ridiculous despite so many sponsors." The Aristotelian 

 account of causation could not be better expressed. Santayana puts 

 this description of it into the mouth of Avicenna in his imaginary 

 dialogue, and makes him go on to say, "Thus these learned babblers 

 would put nature together out of words, and would regard the four 

 principles of interpretation as forces mutually supplementary com- 

 bining to produce material things ; as if perfection could be one of 

 the sources of imperfection or as if the form which things happen 

 to have could be one of the causes of their having it. Far differently 

 do these four principles clarify the world when discretion conceives 

 them as four rays shed by the light of an observing spirit". In this 

 last observation we may perhaps trace the germ of the Copernican 

 revolution in philosophy effected by Kant, if we may take it to enclose 

 the idea of the activity of the experient subject in all perception. 



In science generally, however, the x\ristotelian conceptions went 

 without serious contradiction, and thus formed the framework for all 

 the embryological work that was done, as, for instance, by Albertus 

 Magnus. Owing to its association with the idea of the plan of a 

 divine being, the final cause tended in the Middle Ages to eclipse 

 the others. In the seventeenth century this feeling is well shown in 

 a remarkable passage, which occurs in the Religio Medici of Sir Thomas 

 Browne: "There is but one first cause, and four second causes of all 

 things; some are without Efficient, as God; others without Matter, as 

 Angels; some without Form, as the first matter; but every Essence 

 created or uncreated, hath its Final cause, and some positive End both 

 of its Essence and Operation ; this is the cause I grope after in the 

 works of Nature ; on this hangs the providence of God ; to raise so 



