ON GENERATION. 345 



instrument, and an act having motion ; as in works of art the 

 instruments are moved, for in them, in some sort, the motion 

 of the art exists." 



By these words he seems to imply, that generation is owing 

 to the motion of a certain quality. Just as in art, though the 

 first cause (the " ratio operis ") be in the mind of the artist, 

 yet afterwards, the work is effected by the movement of the 

 hands or other instruments ; and although the first cause be 

 removed (as in automatons,) yet is it in some sort said to 

 move what it now does not touch, but once has touched, so 

 long as motion continues in the instrument. 



Also in the next book, he says : " When the semen of the 

 male has arrived as far as the uterus of the female, it arranges 

 and coagulates the purest part of the excrement (meaning the 

 menstrual blood existing in the uterus) ; and, by a motion of 

 this kind, changes the material, which has been prepared in 

 the uterus, till it forms part of the chick ; and this, hereafter, 

 although the semen after the performance of this motion dis- 

 appears, exists as part of the foetus, and becomes animate (as the 

 heart,) and regulates its own powers and growth, as a son 

 emancipated from his father, and having his own establish- 

 ment. And so it is necessary that there be some commencing 

 principle, from which afterwards the order of the limbs may be 

 delineated, and a proper disposition made of those things that 

 concern the absolution of the animal ; a principle, which may 

 be the source of growth and motion to all the other parts ; the 

 origin of all, both similar and dissimilar parts, and the source 

 of their ultimate aliment. For that which is already an 

 animal grows, but the ultimate aliment of an animal is the 

 blood, or something corresponding to the blood, whose vessels 

 and receptacles are the veins ; wherefore, the heart is the 

 origin of the veins. But veins, like roots, spread to the uterus, 

 and through these the foetus derives its nourishment. The 

 heart too, being the beginning of all nature and the containing 

 end, ought to be made first ; as if it were a genital part by its 

 own nature, which, as the original of all the other parts, and 

 of the whole animal, and of sense, must needs be the first ; 

 and by its heat, (since all the parts are in the material poten- 

 tially^) when once the beginning of the motion has taken 

 place, all that follows is excited, just as in spontaneous 



