23 FUNCTIONS OF THE VITAL SPIRITS. [i. 



ciprocal actions of the brain and nerves on each other, derives 

 great probability from all observation of the operations of the 

 animal forces, and takes place so quickly and immediately, 

 that the fluid acts with inconceivable rapidity, either as to its 

 own movements, or in propagating impressions (Haller, § 381), 



20. It is a natural inference, and one established by facts, 

 that the vital spirits are diminished, or rendered unfit for their 

 functions, by frequent or prolonged use; and, consequently, 

 the animal forces, of which they are the medium, become 

 weakened or disappear (17, 18), or increase, when they are sup- 

 plied to the brain and nerves. 



21. If the vital spirits are duly secreted from the blood in 

 the brain, and their influence goes uninterruptedly thence to 

 the nerves, or vice versa, the functions of the sentient forces or 

 the nerve-forces, of which they are the medium, are performed 

 naturally; and, consequently, those forces can act freely, so 

 far as they are influenced by the vital spirits. 



22. The free action of the animal-sentient or nerve-forces, 

 in so far as it is dependent on the vital spirits, is prevented 

 by whatever prevents the production of the vital spirits in the 

 brain ; by whatever destroys their normal, but to us unknown, 

 condition ; by whatever interrupts their influence directed from 

 the brain to the nerves, or vice versa ; or, finally, by whatever 

 destroys them or wears them out. Obstruction of the cerebral 

 circulation, the compression or destruction of the brain, or its 

 entire removal from the body, prevent the production of vital 

 spirits. A general corruption of the fluids must also neces- 

 sarily destroy their natural condition; ligature, or compression, 

 or section of the spinal cord, prevents their influence being 

 communicated from the brain to the nerves, or from the nerves 

 to the brain ; and an undue straining of the powers of body 

 and mind consumes the vital spirits (20). 



23. Experience teaches us, that sleep, wine and other spiri- 

 tuous drinks, light nourishing food, the odour of spirituous 

 vapours, ablution of the limbs with spirituous fluids, friction, 

 gentle bodily exercise, mental enjoyment, cheerful society, 

 moderate and agreeable use of the senses, all strengthen and 

 enliven the sentient and nerve-forces ; and it is probable that 

 this occurs either from an increased secretion, or a renewed 

 natui'al good state of the nervous fluid, or from a greater 



