376 FUNCTIONS OF THE NERVOUS SYSTEM, [ch. i. 



the cerebellum are ever flowing, equably and continuously, 

 into the nerves which regulate involuntary movements; but 

 those of the cerebrum tumultuously and irregularly, according 

 as the animal actions are vehemently performed or quiescent. 

 To excite sensation, the spirits flow along the nerves to the 

 brain. He distinguishes between a thick nervous fluid, suit- 

 able to nutrition, and the extremely volatile animal spirits, 

 subservient to sensation and movement, and commingled in the 

 preceding as their vehicle. He maintains, that there are two 

 souls in man, the one rational, the other corporeal ; the latter 

 alone is given to brutes. The corporeal, or brute soul, consists 

 partly of a fiery or sulphureous element, which is located in 

 the blood; and partly of an ethereal element, which is the 

 animal spirit secreted in the cerebrum. That the corporeal soul, 

 thus composed, forms a foetus from the semen of the parents 

 like to the parents, increases with the body, preserves the body 

 until death, causes the perception of sensations in the corpora 

 striata, and thence reflected, excites desires and voluntary 

 movements; in the corpus callosum excites imagination, and 

 in the convolutions memory. It diff'ers from the rational soul 

 in this, that the latter uses the corporeal soul as the instrument 

 whereby it performs all things more quickly and readily in man 

 than they are done in brutes, and because in virtue of the 

 rational soul man is rendered capable of contemplating things 

 not belonging to the senses, as God, angels, himself, infinity, 

 eternity, &c. He explains the unity of the nerves by their 

 communications and connections with each other, or their anas- 

 tomoses, as anatomists term them : and he also explains, that 

 the union of the cerebrum and cerebellum is attained by the 

 tubercula quadrigemina, or nates and testes. As to the loops 

 of nerves with which the arteries here and there are encircled, 

 he states their use to be, to relax or close the arteries, and 

 thus during various emotions of the mind to admit the blood 

 in greater or less quantity to certain parts. He decided that 

 the pineal gland is not the seat of the soul, but a lymphatic 

 gland, having no relation with the substance of the brain, 

 which absorbs lymph, aud carries it ofi* again through other 

 vessels, and keeps the plexus choroides expanded. 



His successors, especially of the school of Boerhaave, em- 

 braced some of these doctrines of Willis, but some were exploded. 



i 



