134 



tmnate strength to surmount this resistance : its strength 

 is in its irritability, or in the power it has of contracting 

 itself on the touch of some liquid. Wherefore to aug- 

 ment the irritability of the heart, is to augment its im- 

 putaive force. 



Fecundation, without doubt, increases this force, and 

 that can alone increase it, since it is only by the inter- 

 vention of it that the germ passes over the narrow limits 

 that it retained in its first state. 



19. The fecundating liquor then is a true stimulus, 

 which being conveyed to the heart of the i*erm, excites 

 it in a powerful manner, and communicates to it a new 

 activity. Herein consists what we may call conception. 

 Motion being once impressed on the little moving body, 

 is there preserved solely by the energy of its admirable 

 mechanism. 



But it is not sufficient that the heart should acquire a 

 force sufficient to surmount the resistance of solids y 

 it is like wise necessary that the fluid which it conveys 

 to them, and winch should nourish them, be propor- 

 tionable to the exceeding fineness of the vessels. Such 

 a blood as ours would not circulate in them. The blood 

 of the embryo is at tirst a w'rtish liquor, it grows yellow 

 by degrees, and afterwards red. The more the impul- 

 sion of the heart dilates, the vessels, the more gross, he- 

 terogeneous, and colouring particles they admit, 



The proliiic liquor then is not a mere stimulus but is 

 likewise a nutricious fluid, appropriated to the extreme 

 delicacy of the germ : it has already discharged the 

 functions of a nutritious fluid in the fecundating indivi- 

 dual*^ has caused its comb, spurs, &c. to grow and give 

 strength to all his parts. 



Being conveyed by the arteries to all the parts, it 

 unites itself to 'he nature of each. From i hence pro- 

 ceeds growth) which we do riot pay a sufficient at- 

 tention to. 



It is not lotig before the chick loses the first foritu 

 Wings, thighs, legs, and feet, spring out from its long 

 tail: every thing is formed and disposed oa u new 



