being always found with it, and never without it: as clearly so in other animals as in the human species; and probably in vegetables though in a still lower degree.[68] That as all the common phenomena of mind, can be accounted for from the known facts of organized matter without the souls, and as none of them can possibly be attributed to the soul without the body, there is no necessity to recur to any gratuitous theory in addition to the visible corporeal frame. That the doctrine of the soul originated in ignorance, and has been supported by imposture; that it involves gross contradictions and insuperable difficulties, and is no more countenanced by true religion than by true philosophy. [67] A _Sensation_ is an impression made by some external object on the Senses; the motion thus excited is propagated along the appropriate nerve, until it reaches the Sensory in the Brain, and it is there and there only, felt or _perceived_. An _Idea_, is a motion in the Brain, excited there either by the laws of association to which that organ is subject, or by some accidental state of the system in general, or that organ in particular, without the intervention of an impression on the Senses ab extra as the cause of it. Such a motion being similar to a sensation formerly excited, and being also felt or perceived is the correspondent _Idea_. [68] Dr. Percival, Dr. Bell in the Manchester Transactions, and Dr. Watson in the last volume of his essays, have made this opinion highly probable. Many additional observations are to be found in Dr. Darwin’s works. I consider it as a theory established.