I30 EMBRYOLOGY IN THE SEVENTEENTH [pt. ii 



triguing personality will be sufficiently familiar to anyone even slightly 

 acquainted with seventeenth-century England, and whose biographic 

 details may be found in John Aubrey, published a work with the 

 following title: Two treatises, in the one of which, The Nature of Bodies, 

 in the other, The Nature of Man's Soule is looked into, in way of discovery 

 of the Immortality of Reasonable Soules. It was inscribed in a charming 

 dedication to his son, and consisted, in brief, of a survey of the whole 

 realms of metaphysics, physics, and biology from a very individual 

 point of view. 



One of Sir Kenelm's principal objects in writing was apparently 

 to attack the old terminology of " qualities " in physics and "faculties " 

 in biology. To say, as contemporary reasoning did, that bodies were 

 red or blue because they possessed a quality of redness or blueness 

 which caused them to appear red or blue to us, or again, to say that 

 the heart beat because it was informed by a sphygmic faculty, or, 

 to take the famous example, that opium sent people to sleep because 

 it contained in it a dormitive virtue, appeared mere nonsense and 

 word-spinning to Digby, "the last refuge of ignorant men, who not 

 knowing what to say, and yet presuming to say something, do often 

 fall upon such expressions". 



Digby, like Galileo and Hobbes, wished to explain all phenomena 

 by reference to two "virtues" only, those of rarity and density, 

 "working by means oflocall Motion". Chapters twenty-three, twenty- 

 four, and twenty-five contain his opinions and experiments in embryo- 

 logy. He begins by opening the question of epigenesis or preforma- 

 tion, practically for the first time since Albert the Great. "Our main 

 question shall be", he says, "whether they be framed entirely at 

 once, or successively, one part after another? And if this latter way, 

 which part first?" He declares for epigenesis, but after a manner 

 of his own, refuting "the opinion of those who hold that everything 

 containeth formally all things". "Why should not the parts be made 

 in generation", he asks, "of a matter like to that which maketh them 

 in nutrition? If they be augmented by one kind of juyce that after 

 severall changes turneth at the length into flesh and bone; and into 

 every sort of mixed body or similar part whereof the sensitive creature 

 is compounded, and that joyneth itself to what it findeth there already 

 made, why should not the same juyce with the same progresse of 

 heat and moisture, and other due temperaments, be converted at 

 the first into flesh and bone though none be formerly there to joyn 



