When one is surprised by some violent passion, if one is careful to reflect upon what one feels in one's entrails and in the other parts of the body where the nerves are embedded, as well as upon the accompanying changes in one's face, and considers that all these different agitations of our nerves are entirely involuntary, happening even despite all the resistance our will can muster against them, one will have little difficulty letting oneself be convinced of the simple explanation just given, of all these relations among the nerves.