56 EMBRYOLOGY IN ANTIQUITY [pt. ii 



forming the flesh." In this account of the formation of the embryo, 

 which seems at first sight a Httle fantastic, there are several interesting 

 things to be remarked. Firstly, there is to be noted throughout it a 

 remarkable attempt at causal explanations and not simply morpho- 

 logical description. The Hippocratic writer is out to explain the 

 development of the embryo from the very beginning on machine-like 

 principles, no doubt unduly simplified, but related directly to the 

 observed properties of fire and water. In this way he is the spiritual 

 ancestor of Gassendi and Descartes. The second point of interest is 

 that he speaks of the embryo drying up during its development, a 

 piece of observation which anyone could make by comparing a 

 fourth-day chick with a fourteenth-day one, and which we express 

 to-day in graphical form (see Fig. 220). Thirdly, the ascription of the 

 main driving force in development to fire has doubtless no direct 

 relation to John Mayow's discovery, two thousand years later, that 

 there is a similarity between a burning candle and a living mouse 

 each in its bell-jar, and may mean as much or as little as Sir Thomas 

 Browne's remark, "Life is a pure flame, and we live by an invisible 

 sun within us". Yet the essential chemical aspect of living matter 

 is oxidation, and the development of the embryo no less than the 

 life of the adult is subject to this rule, so that what may have been 

 a mere guess on the part of the Hippocratic writer, may also have 

 been a flash of insight due to the simple observation which, after all, 

 it was always possible to make, namely, that both fires and li\dng 

 things could be easily stifled. 



Preformationism is perhaps foreshadowed in Section 26 of the 

 same treatise. "Everything in the embryo is formed simultaneously. 

 All the limbs separate themselves at the same time and so grow, none 

 comes before or after other, but those which are naturally bigger 

 appear before the smaller, without being formed earlier. Not all 

 embryos form themselves in an equal time but some earlier and some 

 later according to whether they meet with fire and food, some have 

 everything visible in 40 days, others in 2 months, 3, or 4. They 

 also become visible at variable times and show themselves to the 

 light having the blend (of fire and water) which they always will 

 have." 



The work on Generation is equally interesting. The earlier sections 

 deal with the differences between the male and the female seed, and 

 the latter is identified with the vaginal secretion. Purely embryological 



