The character of the secondary sensory elements stands out clear and independent in the phenomena of synaesthesia, of secondary sensations. In the phenomena of synaesthesia we have a sensation of one sense organ followed, without an intermediary direct stimulation, by a sensation coming from another sense organ. Thus, when a sensation of light instead of giving rise to a subsequent idea gives rise to a sensation of sound, for instance, we have the phenomenon of secondary sensation. Here the secondary sensations stand out free and distinct, but they are really always present in our ordinary perceptive experiences as bound up secondary sensory elements, as secondary sensations grouped round primary sensations. When the phenomena of synaesthesia were first brought to the notice of the scientific world, they were regarded as abnormal and exceptional, and only present in special pathological cases. Soon, however, their field became widened, and they were found not only in the insane and degenerate, but in many persons otherwise perfectly normal. We find now that we must further widen the field of secondary sensory elements, and instead of regarding them as a freak of nature existing under highly artificial conditions, we must put them at the very foundation of the process of perception. Secondary sensations are at the basis of perception. We have become so accustomed to them that we simply disregard them. When, however, the conditions change, when the secondary sensations stand out by themselves, isolated from the primary nuclear elements with which they are usually organically synthesized into a whole, into a percept, when they become dissociated, it is only then that we become conscious of them directly and declare them as abnormal. Secondary sensations are always present in every act of perception; in fact, they form the main content of our perceptual activity, only we are not conscious of them, and it requires a special analysis to reveal them. Secondary sensations _per se_ are not something abnormal--just as hydrogen present in the water we drink or the oxygen present in the air we breathe are not newly created elements,--it only requires an analysis to discover them. If there be any abnormality about secondary sensations, it is not in the elements themselves, but rather in the fact of their dissociation from the primary nuclear elements.