ON GENERATION. 503 



admirable qualities of the blood, have imagined other spirits 

 of an aerial or ethereal nature, or composed of an ethereal or 

 elementary matter, a something more excellent and divine than 

 the innate heat, the immediate instrument of the soul, fitted 

 for all the highest duties. Now their principal motive for this 

 was the consideration that the blood, as composed of elements, 

 could have no power of action beyond these elements or the bodies 

 compounded of them. They have, therefore, feigned or imagined 

 a spirit, different from the ingenerate heat, of celestial origin 

 and nature ; a body of perfect simplicity, most subtile, attenu- 

 ated, mobile, rapid, lucid, ethereal, participant in the qualities 

 of the quintessence. They have not, however, anywhere de- 

 monstrated the actual existence of such a spirit, or that it was 

 superior to the elements in its powers of action, or indeed that 

 it could accomplish more than the blood by itself. We, for 

 our own parts, who use our simple senses in studying natural 

 things, have been unable anywhere to find anything of the 

 sort. Neither are there any cavities for the production and 

 preservation of such spirits, either in fact or presumed by their 

 authors. Fernelius, indeed, has these words : l "He who has 

 not yet completely mastered the matter and state of the inge- 

 nerate heat, let him cast an eye upon the structure of the 

 body, and turn to the arteries, -and contemplate the sinuses of 

 the heart and the ventricles of the brain. When he observes 

 them empty, containing next to no fluid, and yet feels that he 

 must own such parts not made in vain, or without a design, he 

 will soon, I conceive, be brought to conclude that an extremely 

 subtile aura or vapour fills them during the life of the animal, 

 and which, as being of extreme lightness, vanished insensibly 

 when the creature died. It is for the sake of cherishing this aura 

 that by inspiration we take in air, which not only serves for the 

 refrigeration of the body, by a business that might be other- 

 wise accomplished, but further supplies a kind of nourishment." 

 But we maintain that so long as an animal lives, the cavities 

 of the heart and the arteries are filled with blood. We fur- 

 ther believe the ventricles of the brain to be indifferently fitted 

 for any so excellent office, and that they are rather formed for 

 secreting some excrementitious matter. What shall we say, 



1 Physiologia, lib. iv, cap. 2. 



