158 EMBRYOLOGY IN THE SEVENTEENTH [pt. 11 



confused. It suffers from containing in its earlier part a great deal 

 of matter which really belongs to the physiological text-book which 

 immediately preceded it. Thus it begins abruptly in the middle of 

 a disquisition on the error of attributing bodily functions to the soul. 

 Before long, however, it warms to its theme, and a conception of 

 growth is outlined. "When one is young, the movement of the little 

 threads which compose the body is less slow than it is in old age, 

 because the threads are not so tightly joined one to the other, and 

 the streams in which the solid particles run are large, so that the 

 threads become attached to more matter at their roots than detaches 

 itself from their extremities, so that they grow longer and thicker, 

 in this way producing growth." The fourth part of the book is called, 

 strangely enough, a Digression, in which the formation of the animal 

 is spoken of. The mixture of seeds is then described, and a theory 

 of the formation of the heart is attempted by means of an analogy 

 with fermentation. The explanation is unconvincing, but has a cer- 

 tain interest as showing chemical notions beginning to permeate 

 biological thought. However, Descartes' way of looking at develop- 

 ment was thoroughly novel, as is illustrated by the following citation. 

 "How the heart begins to move.. . .Then, because the little parts 

 thus dilated, tend to continue their movement in a straight line, and 

 because the heart now formed resists them, they move away from it 

 and take their course towards the place where afterwards the base 

 of the brain will be formed, they enter into the place of those that 

 were there before, which for their part move in a circular manner 

 to the heart and there, after waiting for a moment to assemble 

 themselves, they dilate and follow the same road as the aforemen- 

 tioned ones, etc." Descartes, in fact, with premature simplification, 

 was trying to erect an embryology more geometrico demonstrata. 

 That he failed in the attempt was as obvious to his contemporaries 

 as it is to us — "We see", said Garden, "how wretchedly Descartes 

 came off" when he began to apply the laws of motion to the forming 

 of an animal". In doing so, he was many years before his time; 

 Borelli had done all that could be done at that period in that direc- 

 tion, and, significantly enough, he left embryology alone. The rest 

 of Descartes' book is exactly like the citations which have been given, 

 only applied to each organ and part in turn; he practically uses the 

 traditional teaching as a scaffolding in which to interweave his 

 mechanical theory, and he discovers no new facts. 



