Many authors have already discovered a number of difficulties resulting from the opinion which makes the nerves the exclusive seat of sensibility, they have even sought for other means of explaining the phenomena of great living bodies. But of its agents we know as little as we do of its nature, and have no means of elucidating questions of this sort. Let us be contented with analyzing, collecting and comparing facts with seizing their general results; the aggregate of these researches will compose the true theory of the vital powers; the rest is only conjecture: but besides the considerations which I have offered, there is another which manifestly goes to prove that the organic functions are not under the immediate influence of the brain, and this is, that the viscera, which perform such functions do not receive their nerves from the brain but from the ganglions. This anatomical fact is observable in the liver, the kidney, the spleen, pancreas, intestines, &c. even in the organs of the animal life there are nerves which serve for the external, and nerves which serve for the internal functions. In such the former come directly from the brain, the latter from the ganglions. Thus the ciliary nerves, which come off from the opthalmic ganglion, are those which preside over the secretions and nutrition of the eyes, the optic nerve which is derived from the brain is the nerve of vision.[120] In the same way the olfactory nerves of the pituitary membrane are the agents by which we have the perception of odours, the threads which come off from the ganglions of Mekel, relate only to the organic phenomena of the membranes. Now the nerves of the ganglions cannot transmit the action of the brain; for we have seen that the nervous system derived from these bodies should be considered as entirely independent of the nervous system of the brain; and that the great sympathetic does not derive its origin from the brain, from the spinal marrow, or from the nerves of the animal life; but from the ganglions exclusively; this nerve indeed does not exist, it is only the aggregate of so many small nervous systems as there are ganglions, which are the particular centres of the organic life, just in the same way as the brain is the great and only centre of the animal life.