The brain also eminently enjoys this property, and not only retains the impressions it receives but propagates their actions, by communicating the vibrations to the nerves. The organs of the exterior senses, the brain, the spinal marrow, and the nerves, which are diffused over every part of the body, ought to be considered as one continued substance, as an organic machine, in which the senses are the parts acted upon by the external objects. But what renders this machine so different from all others is its fulcrum not only being capable of resistance and re-action, but is itself active, because it long retains impressions it has received; and the brain and its membranes being of great capacity and sensibility, it may receive a number of successive agitations, and retain them in the order in which they were received, because each impression agitates one part of the brain only, and the successive impressions agitate the same or contiguous parts, in a different manner. Should we suppose an animal which had no brain, but possessing an exterior of great sensibility and extension; an eye, for example, of which the retina was as extensive as that of the brain, and had the property of retaining, for a long space, the impressions it might receive: it is certain, that the animal so endowed would see at the same time not only the present objects, but also those it had seen before; and seeing thus the past and the present with one glance, it would be determined mechanically to act according to the number or force of the agitations produced by the images which accorded with, or were contrary to this determination. If the number of images calculated to create an appetite surpassed those that would produce disgust or loathing, the animal would necessarily be determined to move, in order to satisfy that appetite: but if their number and force were equal, having no particular cause for motion, it would remain perfectly at rest; and if the number or the force of the images of the former are equal to the number or the force of the images of the latter, the animal will remain undetermined, and in an equilibrium between these two equal powers, nor will he make any movement either to obtain or to avoid. This I say it would do mechanically, and without the intervention of memory; for as the animal sees at the same time all the images, they consequently act, and those which have an affinity to appetite and desire, counteract those which have an affinity to antipathy and disgust; and it is by the preponderance of either, that determines it to act in this or in that manner.