284 The Older Doctrines [lect. 



contraction itself, more true and exact than those even of 

 Borelli. He laid hold more clearly than Borelli seems to have 

 done of the truth that the contraction of a muscle is the 

 result of the contraction of the individual fibres ; and he quotes 

 the experiment that when a long muscle is cut up lengthways 

 by scissors in three or four bits, each bit may be made to 

 contract, as a proof that the power of contraction resides in the 

 muscular substance as substance and not in the whole muscle 

 as a machine. He further states that contraction is not de- 

 pendent on the action of arteries, or veins, or even necessarily 

 on that of nerves; and he insists that while all voluntary 

 movement is brought about by muscles, every movement which 

 a muscle carries out is not necessarily a voluntary one. He 

 ends his essay on muscle with the following remarkable 

 speculation : 



" Concerning the fluid of muscles how uncertain, or rather 

 " how wholly wanting is our knowledge. Fluid certainly exists 

 "in the fibrillae of which the motor fibres are composed and 

 " between the fibrillae, also between the motor fibres themselves, 

 " in the membranous fibrillae " (that is the connective tissue), 

 "and between the membranous fibrillae; but in truth it is by 

 "no means clear whether these fluids are all of one kind or 

 "whether just as they are distinct in the seats which they 

 "occupy so they differ in material properties. 



" Nor is it known whether any of these fluids are really like 

 " any one of the fluids so far known to us. Animal spirits, the 

 " more subtle part of the blood, the vapour of blood, and the 

 "juice of the nerves, these are names used by many, but they 

 " are mere words, meaning nothing. Some going further bring 

 " forward saline and sulphureous particles or something ana- 

 " logous to spirits of wine. Such things may perhaps be true, 

 " but are neither certain nor adequately distinct. Experience 

 "teaches us that a dose of spirits of wine restores exhausted 

 "powers, but who shall have determined whether that which 

 " restores the fluid spirit is to be ascribed to this said humour 

 " which we call spirit or to some other material or is joined to 

 " it through some other cause ? 



" As the substance of this fluid is unknown to us, so is its 



