296 The Older Doctrines [lect. 



The first subject which he discusses, 'by conjectures/ is the 

 nature of nervous action. He expounds and rejects the view- 

 put forward under various shapes that the nerves act as solid 

 bodies, after the fashion, for instance, of elastic strings along 

 which vibrations are conveyed. In his encyclopaedic manner 

 he recalls and discusses various views of this kind put forward 

 by various men, including that of Nicolas Robinson, who in 

 his work on the spleen supposed that the nerves of sense were 

 composed of little papillary machines, exceedingly small and 

 exceedingly numerous and minute, which struck by the object 

 giving rise to the sensation were thrown into oscillations and 

 so conveyed the impression to the mind. 



He next discusses the view that nervous action depends 

 upon a fluid. 



" All the ancients attributed to the nerves a most subtle and 

 " attenuated humour or rather fluid, for the word humour 

 " suggests something sluggish, to which they gave the name of 

 "spirits, and which, though invisible just like air, exercises a 

 " great power. This doctrine of the schools for many ages held 

 " its place ; lately, however, this doctrine of spirits, like all other 

 "things which pleased of old, began to totter. Then a sect 

 " by no means weak " (namely that of Stahl) " took up the posi- 

 tion that the soul acted directly hand to hand in all the 

 "actions of the body and did not make use of instruments, 

 " by which it conveyed its commands to distant parts. People 

 "began to doubt very much about these spirits, and indeed 

 "now even the most distinguished men share these doubts." 



He first marshals all that can be said against this hypo- 

 thesis of the spirits, that is of the active part of the nerve 

 being of the nature of a fluid, quoting among other things 

 the argument that a nerve when ligatured does not swell, 

 and the like. But he finds these objections invalid ; and 

 assuming therefore that the active nervous material is of 

 a fluid nature, he proceeds to discuss what must be its 

 essential characters. These lead him to the conclusion that 

 it cannot be of the nature of an albuminous solution, nor 

 spirituous in nature like alcohol, nor acid, nor sulphureous, 

 i.e. combustible. He likewise decides that it cannot be, as so 



