At no time does Nature furnish us with any proof of bodies existing in a state of absolute rest. The whole molecular world, organic as well as inorganic, is, as far as we can ascertain, in constant motion. In consequence of this well-established principle, every function of the body may rightly be considered as resulting from a change in the molecular state of the organ manifesting such, and as being the expression of a correlative variation occurring in its representative nerve centre. Through the agency of long continuance the visceral disturbances are now carried on in a somewhat automatic manner, and fail to excite any feeling of their existence, although they may at one time, in the evolution of higher organisation have produced a conscious sensation.