"This general and imperfect sketch of the anatomy of the nervous system relates only to what may be discovered by our unassisted sight. If by means of the microscope we endeavour to observe the ultimate nervous fibres, persons in general are as much at a loss as when, by the same means, they attempt to trace the ultimate muscular fibres[42]." ILLUSTRATION, OF MOTION NOT NECESSARILY IMPLYING SENSATION. "Assuredly, motion does not necessarily imply sensation; it takes place where no one ever yet imagined there could be sensation. If I put on the table a basin containing a saturated solution of salt, and threw into it a single crystal, the act of crystallization would begin from the point touched, and rapidly and regularly pervade the liquor till it assumed a solid form. Yet I know I should incur your ridicule if I suggested the idea that the stimulus of salt had primarily excited the action, or that its extension was the effect of continuous sympathy. If, also, I threw a spark amongst gunpowder; what would you think, were I to represent the explosion as a struggle resentful of injury, or the noise as the clamorous expression of pain[43]?" DIFFERENT NERVOUS SYSTEMS VARIOUSLY AFFECTED BY SIMILAR IMPRESSIONS. "Thus the odour of a cat, or the effluvia of mutton, the one imperceptible, the other grateful to the generality of persons, has caused individuals to fall on the ground as though bereaved of life, or to have their whole frame agitated by convulsions. Substances which induce disease in one person or animal, do not induce disease in others[44]." IMPORTANCE OF OPINIONS. "Thinking being inevitable, we ought, as I said, to be solicitous to think correctly. Opinions are equally the natural result of thought, and the cause of conduct. If errors of thought terminated in opinions, they would be of less consequence; but a slight deviation from the line of rectitude in thought may lead to a most distant and disastrous aberration from that line in action. I own I cannot readily believe any one who tells me he has formed no opinion on subjects which must have engaged and interested his attention. Persons both of sceptical and credulous characters form opinions, and we have in general some principal opinion, to which we connect the rest, and to which we make them subservient; and this has a great influence on all our conduct. Doubt and uncertainty are so fatiguing to the human mind, by keeping it in continual action, that it will and must rest somewhere; and if so, our inquiry ought to be where it may rest most securely and comfortably to itself, and with most advantage to others. "In the uncertainty of opinions, wisdom would counsel us to adopt those which have a tendency to produce beneficial actions." INDEPENDENCE OF MIND ON LIFE AS ARISING OUT OF THE IDEA THAT LIFE WAS SUPERADDED TO ORGANIZATION—HIS DISPOSITION TO ALLEGORY.