The recognition of the transformation in dream life of internal sensations into symbolic motor imagery is ancient. Hippocrates said that to dream, for instance, of springs and wells denoted some disturbance of the bladder. In such a case a disturbed bladder sends to the brain, not the naked message of its own needs, but a symbolic message of those needs in motor imagery, as (in one case known to me) of a large cistern with a stream of water flowing from it.[151] Sometimes the symbolism aroused by visceral processes remains physiological; thus indigestion frequently leads to dreams of eating, as of chewing all sorts of inedible and repulsive substances, and occasionally--it would seem more abnormally--to agreeable dreams of food. It is due to the genius of Professor Sigmund Freud, of Vienna--to-day the most daring and original psychologist in the field of morbid psychic phenomena--that we owe the long-neglected recognition of the large place of symbolism in dreaming. Scherner had argued in favour of this aspect of dreams, but he was an undistinguished and unreliable psychologist, and his arguments failed to be influential. Freud avows himself a partisan of Scherner's theory of dreaming and opponent of all other theories,[152] but his treatment of the matter is incomparably more searching and profound. Freud, however, goes far beyond the fundamental--and, as I believe, undeniable--proposition that dream-imagery is largely symbolic. He holds that behind the symbolism of dreams there lies ultimately a _wish;_ he believes, moreover, that this wish tends to be really of more or less sexual character, and, further, that it is tinged by elements that go back to the dreamer's infantile days. As Freud views the mechanism of dreams, it is far from exhibiting mere disordered mental activity, but is (much as he has also argued hysteria to be[153]) the outcome of a desire, which is driven back by a kind of inhibition or censure (_i.e._, that kind of moral check which is still more alert in the waking state), and is seeking new forms of expression. There is first in the dream the process of what Freud calls condensation (_Verdichtung_), a process which is that fusion of separate elements which must be recognised at the outset of every discussion of dreaming, but Freud maintains that in this fusion all the elements have a point in common, and overlie one another like the pictures in a Galtonian composite photograph. Then there comes the process of displacement or transference (_Verschiebung_), a process by which the really central and emotional basis of the dream is concealed beneath trifles. Then there is the process of dramatisation or transformation into a concrete situation of which the elements have a symbolic value. Thus, as Maeder puts it, summarising Freud's views, 'behind the apparently insignificant events of the day utilised in the dream there is always an important idea or event hidden. We only dream of things that are worth while.