be in causal relation with a former similar idea. Place and time of this former idea may likewise be fixed by means of the accompanying circumstances of the same surging up in memory.

It is thus nothing but the comparison of a present and a past representation, that determines the unity of consciousness between temporally separated moments. The possibility of this comparison is attained by this: that of two present ideas the one represents the present, the other the past; and the latter again becomes possible by this: that I know the present idea to be in causal connection. with a former one similar to it. While, now, of the two ideas, the one represents the past, consciousness comprehends in this indivisible act of comparison the representations of the present and past consciousness into one, and therewith becomes conscious of the unity of consciousness for that past and the present representation. To wit, if I have two conscious representations, there exists a consciousness of the one and a consciousness of the other idea; and I should never have the right of maintaining a unity of these two consciousnesses if I could not prove it. But now, when I bring together two ideas for comparison, I merge both consciousnesses in the third consciousness of the comparison, and in this way have brought their unity to immediate intuition. The comparison is thus the moment which first of all makes possible the thought of a unity of consciousness, and with the possibility of comparison the possibility of the unity of consciousness also

ceases.

As we have here seen the act of comparison to be the judge of the unity of consciousness of a past and a present, i.e., temporally separate representations, so does it also decide in respect of spatially separated ideas, ie., such as are excited by different material parts. A human brain has a certain magnitude, and the representations which arise at one end of it are many inches removed from those arising at the other end; nevertheless we do not doubt the

unity of the cerebral consciousness. The reason is simply this: that in the healthy waking state every idea arising anywhere in the brain may be compared with any one arising anywhere else. On the other hand, the ideas of the spinal cord and the ganglia, as they must of necessity exist in reflex movements, &c., in injuries of the viscera and the like, have in general no unity of consciousness along with the cerebral representation; they have rather each their separate conscious existence, since they cannot be taken up into a common conscious act of comparison. Only a few strong sensations of the lower nerve-centres are comparable, and a unity of consciousness possible so far as it is exhibited in common feeling. Whilst for the different nerve-centres of an organism this unity of consciousness is established with stronger stimulation of the one or the other, it is in no way to be established for the nerve-centres of different individuals, unless with partial coalescence of two organisms by abortion, or between mother and foetus, where echoes of such unity of consciousness are found for strong stimulations.

The cause of these phenomena is obvious. In the brain, beside the special commissures, innumerable nervefibres traverse the whole mass and establish a manifold intimate union of every particle with the rest; the spinal cord has already a much more imperfect union with the brain; the sympathetic nervous system is only connected with it by the single nervus vagus. In individuals which have grown together only more or less casual concrescence of subordinate nerve-strands can take place; in the case of separate individuals all union is wanting. The more perfect is the path between the functional part of the central nerves, the less stimulus it needs to propagate the stimulus of the one to the other unenfeebled and undisturbed; the more imperfect and longer the paths of conduction, the greater the resistances, the stronger must be the stimuli, if they are to be propagated to the other central spot, and the more obscure and more effaced are they on arrival.

For him who is accustomed to the endless intermingling of the phenomena of physical vibrations without any mutual disturbance, this mode of viewing the nervous processes, according to which each thought at one spot of the brain is simultaneously telegraphed to all other spots, will not appear strange; it is impossible to interpret the anatomical construction of the brain with its numerous connecting fibres in any other manner. The capability of conduction it is then, in fact, which physically conditions the unity of consciousness, and with which this is proportional. We lay down, then, as a principle: Separate material parts give separate consciousness, a proposition which is as much recommended à priori as the distinct individuals confirm it empirically. As long as the Australian ant is an animal, its fore and after body acts with undivided consciousness; as soon as one has cut it in pieces, the unity of consciousness is abolished, and both parts turn against one another. We further assume: the comparison of two ideas produced at different places only becomes possible by the vibrations of the one place being carried over to the other unenfeebled and undisturbed; only by the comparison of the two representations is the abolition of their two consciousnesses in the indivisible consciousness of the act of comparison possible; with it, however, we may add, it is also eo ipso given. (The metaphysical condition of the identity of the psychical unconscious substance, which will be discussed in Sect. C. Chap. vii., is here, of course, tacitly assumed. Without it the physical condition of nerve-conduction would be just as vague as the former without the latter.) The Siamese twins refused to play draughts with one another, thinking that this would be as if the right hand should play with the left. The negresses coadjunct at the lower part of the back, who allowed themselves to be exhibited at the beginning of 1873 in Berlin, under the name of the two-headed nightingale, are said to have sympathetic feelings of their mutual sensations in the lower extremities., i.e., possess a unity of

consciousness with respect to a certain sensitive area in spite of the duality of their persons. But if one imagined. the union of the brains of two men possible by a bridge as capable of conduction as is that between the two hemispheres of the same brain, a mutual and indivisible consciousness, including the thoughts of both brains, would immediately embrace the hitherto separate consciousnesses of both persons; each would no longer be able to distinguish his own thoughts from those of the other; ie, they would no longer know themselves as two Egoes, but only as one Ego, as my two cerebral hemispheres also only know themselves as one Ego.

IV.

THE UNCONSCIOUS AND CONSCIOUSNESS IN THE VEGETABLE KINGDOM.

THE question of the animation of the vegetable kingdom. is an old one; outside Judaism and Christianity it has been almost everywhere affirmed. Our time, which has been nourished by the theories of these two systems of belief, and has not yet by a long way bridged over the gulf between spirit and sense, rent asunder by Christianity, has with difficulty admitted the kinship of men and animals; no wonder that it has not yet been able to elevate itself to the admission of the vegetable soul, since its physiology is accustomed to regard, even in the animal, the organic functions and reflex actions as merely material mechanisms. The subject has been best treated by Fechner in his memoir, "Nanna; or, The Psychical Life of Plants" (Leipzig, 1848), if also with an infusion of much of the fantastical; comp. further Schopenhauer, "On Will in Nature," chap. "Vegetable Physiology," and Autenrieth, "Views on Nature and Psychical Life." I shall content myself with giving a short exposition of the doctrine, and with showing the considerably greater clearness which is introduced into the whole question by the distinction of unconscious and conscious psychical activity. I am convinced that many a one, who was obliged to maintain a negative position owing to the previous mode of treatment, will be reconciled to the doctrine of plant-animation when the notions of the Unconscious and Consciousness are kept quite apart.