With reference to Dr. Nichols's carefully elaborated theory I have little to say, except to note the danger of trusting overmuch to results obtained from such combinations of hypotheses as one must make use of in biological retrospect. The danger is illustrated in the fact that the very number of this Review which contains the first part of Dr. Nichols's article contains also an argument by Mr. Stanley showing grounds for a position exactly opposite in one respect to that taken by the former. Dr. Nichols holds pleasure to have been the primal sense. Mr. Stanley, on the other hand, holds pain to have been the primal sense. There is a difficulty in reference to both of these theories, viz.: that if Pain and then Pleasure, or Pleasure and then Pain, be supposed to be the originally differentiated sensations from which all others have been developed, we should certainly look for their disappearance in the process of development or else for a distinct common-sense division of all sensational phenomena on lines of pleasure and pain; and this we nowhere find. Dr. Nichols does not make clear to me what may be the mechanism by which the hypothetical pleasure nerves bring about "the neural activities whose function is to continue certain beneficial processes," or that by which the pain nerves bring about the "neural activities whose function is discontinuance." Apparently the continuance and discontinuance must refer to the organ which is functioning in direct connection with the pain and pleasure activities, and as we must postulate, I presume, one brain centre for pain and one for pleasure to regulate this discontinuance and continuance in an indefinite number of directions, it would appear to be necessarily by means of some direct return motor (?) activity to the functioning organ; but how it is to act upon the organic function which is to be discontinued or continued, I do not understand. Can it be inhibitively in the case of pain and in manner to duplicate the stimulus in the case of pleasure?
I have above presented all arguments of moment which to my knowledge have been brought forward to substantiate the view that Pleasure and Pain are to be classified with Sensation. It seems to me that any unbiassed observer must grant that the utmost that can be claimed for these arguments is that they furnish ground for the provisional acceptance of the view in question as a working hypothesis unless objections to the acceptance of the hypothesis appear in other directions. But it seems to me that very formidable objections do appear as soon as the matter is taken into full consideration. Some of these I wish now to lay before the reader.
