15. By touching the hairs on the back of the hand, you can stimulate the "pressure spots." 16. By pricking the skin with the point of a needle, you can stimulate the "pain spots." 17. The sense of taste is sensitive only to solutions that are sweet, sour, salt, or bitter. Plan experiments to verify this point. What we call the "taste" of many things is due chiefly to odor. Therefore in experiments with taste, the nostrils should be stopped up with cotton. It will be found, for example, that quinine and coffee are indistinguishable if their odors be eliminated by stopping the nose. The student should compare the taste of many substances put into the mouth with the nostrils open with the taste of the same substances with the nostrils closed. REFERENCES FOR CLASS READING COLVIN AND BAGLEY: _Human Behavior_, Chapters VII and XII. MÜNSTERBERG: _Psychology, General and Applied_, Chapters III, IV, VI, and VII. PILLSBURY: _Essentials of Psychology_, Chapters II, III, and IV. PYLE: _The Outlines of Educational Psychology_, Chapter II. TITCHENER: _A Beginner's Psychology_, Chapter I, par. 3; also Chapter II. CHAPTER IV INHERITED TENDENCIES =Stimulus and Response.= We have learned something about the sense organs and their functions. We have seen that it is through the sense organs that the world affects us, stimulates us. And we have said that we are stimulated in order that we may respond. We must now inquire into the nature of our responses. We are moving, active beings. But how do we move, how do we act when stimulated? Why do we do one thing rather than another? Why do we do one thing at one time and a different thing at another time? Before we answer these questions it will be necessary for us to get a more definite and complete idea of the nature of stimulus and response. We have already used these terms, but we must now give a more definite account of them. It was said in the preceding chapter that when a muscle contracts, it must first receive a nerve-impulse. Now, anything which starts this nerve-impulse is called the stimulus. The muscular movement which follows is, of course, the response. The nervous system forms the connection between the stimulus and response. The stimulus which brings about a response may be very simple. Or, on the other hand, it may be very complex. If one blows upon the eyelids of a baby, the lids automatically close. The blowing is the stimulus and the closing of the lids is the response. Both stimulus and response are here very simple. But sometimes the stimulus is more complex, not merely the simple excitation of one sense organ, but a complicated stimulation of an organ, or the simultaneous stimulation of several organs. In playing ball, the stimulus for the batter is the on-coming ball. The response is the stroke. This case is much more complex than the reflex closing of the eyelids. The ball may be pitched in many different ways and the response changes with these variations.