The Clifford Lectures Edinburgh 1937-8
VIII. The Organ of Liaison
...Galvani, chastened by Volta's criticism, was actually ushering in the modern reading of the animal spirits, when at Konigsberg a laborious anatomist, Sommerring, had an idea. He had published many drawings of the gross anatomy of the brain. He had acquired merit by renumbering yet once more though incorrectly the cranial nerves. Then, at climax of his maturity, he reported the ultimate finding of his toil, to the effect that the soul resides in the water of the brain. He said also, that although he had read widely, he had not met that idea elsewhere! To crown his discovery he dedicated this final work to his fellow-townsman, Immanuel Kant, philosopher.
There were no doubt those who smiled. Kant faced the situation with stoic courtesy. He acknowledged the compliment. He met the request for his opinion by a lengthy letter, addressed to the author. He wrote, ''We are told now by this discovery that the common sensorium is neither more nor less than the water in the chambers of the brain. There it isolates the nerves whose ends pass thither so that the sensations are not confused. It is at the same time a medium of communication between them.'
"A difficulty", he goes on, "is that water is not organized. Without organization no matter can be thought of as providing an organ for the soul. However, if we turn from the mechanical uniformity of water to its chemical composition there is more scope. Water has now been split by pneumatic experiments into two gases [Cavendish, 1781]. Each of these gases besides its own basis has caloric. This latter may be decomposable into light and other material like light, which again is decomposable into colours " , and so on. " A drop of water, a grain of sand, or things even more simple still, are inexhaustible in the diversity of their least parts, even to an understanding so limited as man's."
Plants extract from water a vast quantity of matters. Who knows what the nerves might find to their hand in the water of the brain? "Suppose the nerves in their several kinds can decompose the water in the brain, its elements may give rise to different sensations. The excitation over, the elements might then reunite. Thus, what this book claims might come to pass."
But the seat of the soul? No. "One cannot assign a relation in space to what is determinable only in time. Many fancy they feel their thought in their head, but that is a mistake. The mistake is to infer that the cause of sensation is there where it is experienced. They attribute thought to traces in the brain left by impressions of sense. These supposititious traces carry no inference as to the seat of the soul. It is just material acting as at the common sensorium, as at an antechamber of the mind. Water within the chambers of the brain might truly be a common sensorium. But seat of the soul? No. That leads to √(-2), an impossible quantity."