the organ of taste is benefited by the pleasant sweetness. And so the argument might go on. There is yet another difficulty. “Every pleasure,” says Spencer, “increases vitality; every pain decreases vitality. Every pleasure raises the tide of life; every pain lowers the tide of life.” Yet we read elsewhere that “pleasures are the incentives to life-supporting acts, and pains the deterrents from life-destroying acts.” Pain, then, is thoroughly bad for us, because it is detrimental to life; but pain at the same time is thoroughly good for us, because it prevents our doing what is detrimental to life. Pain as detrimental ought to have been eliminated by natural selection; pain as warning of what is detrimental has been conserved by natural selection. Can the two points of view be reconciled? _It would be foolish and overhasty to reject outright the biological view of feeling_; the very fact that it has lasted through so many centuries and, in some form or other, has appealed to so many psychologists—the quotation which heads this chapter is a case in point!—raises a presumption in its favour. Our conclusion must rather be this: that general formulas, which need to be qualified almost as soon as they are phrased, and which lay themselves open to all kinds of specific objections, cannot help us to a psychology of feeling—or of anything else. When we have found out, by detailed experimental work, what the nervous correlate of simple feeling really is, then we may perhaps advance to some general biological view; but the detailed work must come first. Questions and Exercises (1) Answer the questions printed on pp. 255, 256 of F. Galton’s _Inquiries into Human Faculty and Its Development_ (Everyman’s Library, E. P. Dutton & Co., New York; price 35 cents). When you have answered them, read Galton’s discussion of mental imagery, pp. 57 ff. (You will find many other interesting things in the book; for instance, the discussion of synæsthesia, pp. 105 ff.) (2) Try to secure a memory after-image, (_a_) by glancing attentively at a lamplit study-table, and then closing the eyes; and (_b_) by listening attentively to a short musical phrase or to a dictated sentence. How do you distinguish this image from a positive after-image? (3) Describe the tied images that you find in the following figure. [Illustration] (4) How is it that very great differences in mental imagery may go undetected in everyday life? (5) Try to give instances, from your own experience, (_a_) of the confusion of sensation and image, (_b_) of memory-colours, and (_c_) of the alteration of a perception by an image-complex. (An instance under (_c_) would be, for example, your failure to find something that you had lost, although it lay in plain sight, because you had a mental picture of it, different from its actual look in perception.)