Man's senses, as it has been shewn, are the only means by which he is
enabled to ascertain whether his opinions are true or false, whether his
conduct is useful to himself and beneficial to others, whether it is
advantageous or disadvantageous. But that his senses may be competent to
make a faithful relation--that they may be in a capacity to impress true
ideas on his brain, it is requisite they should be sound; that is to
say, in the state necessary to maintain his existence; in that order
which is suitable to his preservation--that condition which is
calculated to ensure his permanent felicity. It is also indispensable
that his brain itself should be healthy, or in the proper circumstances
to enable it to fulfil its functions with precision, to exercise its
faculties with vigour. It is necessary that memory should faithfully
delineate its anterior sensations, should accurately retrace its former
ideas; to the end, that he may be competent to judge, to foresee the
effects he may have to hope, the consequences he may have to fear, from
those actions to which he may be determined by his will. If his organic
system be vicious, if his interior or exterior organs be defective,
whether by their natural conformation or from those causes by which they
are regulated, he feels but imperfectly--in a manner less distinct than
is requisite; his ideas are either false or suspicious, he judges badly,
he is in a delusion, in a state of ebriety, in a sort of intoxication
that prevents his grasping the true relation of things. In short, if his
memory is faulty, if it is treacherous, his reflection is void, his
imagination leads him astray, his mind deceives him, whilst the
sensibility of his organs, simultaneously assailed by a crowd of
impressions, shocked by a variety of impulsions, oppose him to prudence,
to foresight, to the exercise of his reason. On the other hand, if the
conformation of his organs, as it happens with those of a phlegmatic
temperament, of a dull habit, does not permit him to move, except with