facts. If the vibrations go beyond the common limit of pleasure and pain in one part of the brain, at the same time that they fall short of it in others, the result will be a pleasure or pain, according as this or that sort of vibrations prevails; and if they be nearly equal, it will be difficult to determine of which kind it is. If the vibrations fall a little short in all the parts, they will generate a high degree of pleasure; which, however, must be less than the least general pain, i.e. such a one wherein the vibrations go beyond the limits in all the parts: but it may be far greater than partial pains, or than those which affect only one particular region of the brain. Hence we may see, that the pains are in general greater than the pleasures; but then they are more rare for the same reason, being such violent states as cannot arise from common impressions. Or, if we suppose the pains to be frequent, they will then so far alter the disposition of the medullary substance, according to what was said above, as that many original pains will be converted into pleasures. Which indeed seems to be the case not unfrequently; for the organs of the new-born infant are so delicate, as to receive pain from many of those impressions which afterwards yield pleasure. But then, his sources of pleasure seem to be multiplied more than in proportion to what he suffers by this previous passage through pain.
In certain cases of excessive pains, the violent vibrations appear at last to excite a latent attractive power in the medullary particles, in the manner hereafter to be described, in respect of the fibres of the muscles and membranes, which puts a stop to those very vibrations that excited it. Hence faintings and stupors; i.e. the cessation of pain from violent pains. However, a greater degree of vibrations is probably required for exciting this attractive power in the medullary particles than in white fibres, and in white fibres than in red ones, as will appear hereafter.
It follows also, from the principles here laid down, that all the pleasures, though particularly different from each other, ought to have a general resemblance, in their circumstances and consequences; and the pains likewise.
Seventhly, All the mere sensations, which enter the mind by the five external senses, admit of a general analysis, upon the same principles as the pleasures and pains do. For all the mere sensations were, in their original state, either pleasures or pains; and vary now from their original state only by the diminution of the degree. Let therefore all the differences of kind, place, and line of direction, be combined in all their varieties, the degree being supposed every where evanescent; and we shall have all the particular vibrations from whence each mere sensation arises. This is the general account. But it is a most difficult problem to explain, by what differences of kind the particular sensations, either of the same or of different senses, are distinguished from each other.
