CRITES. If these views be correct, and if your speculation also be correct as to the existence of special organs in the brain for the purposes of locomotion and speech, it would appear probable that there is a special organ for that of memory also.

ERGATES. That is true. But there our knowledge ends. We may, I suppose, take it for granted that there is no animal whose memory is equally capacious with that of man; and we know that, with the exception perhaps of the dolphin (of whose faculties we know nothing), there is no other animal in whom that portion of the cerebrum which we call its hemispheres, and which are bounded externally by the convolutions, is equally developed. It may be said, and not without some show of reason, "Do not these facts seem to indicate where the faculty of memory resides?" Willis answered the question in the affirmative.* But observe how it is in birds. In them there are

*Multiplices cerebri plicæ et convolutiones requiruntur, nempe ut in istis, tanquam in diversis cellulis et apothecis sensibilium species reservari, atque illinc pro datâ occasione evocari queant. — Willis, de Anatome Cerebri, cap. 10.

no convolutions; and the only part of the brain which can be said to correspond to the cerebral hemispheres of man, is merely a thin layer of cerebral substance expanded over some other structures which are developed to an enormous size. Yet we know that birds which are domesticated exhibit signs of considerable memory, parrots and cockatoos recognising individuals after a long interval of time; and that birds in their natural state return to their old haunts after their annual migrations. The exploits of the carrier-pigeons cannot be explained without attributing to them no small powers of observation, and of recollecting what they had observed. Perhaps future observations on the effects produced by disease of the brain in connection with affections of the memory may throw some light on this mysterious subject. At present we must be content to acknowledge that we know nothing as to the locality of the function, nor of the minute changes of organization which are connected with it.

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THE THIRD DIALOGUE.

The Subject of Memory continued. Sequence and Association of Ideas.—Suggestion of Ideas by internal Causes acting on the Brain by the Nerves, or through the Medium of the Blood.-Influence of Narcotics, Morbid Poisons, Lithic Acid, Impure Atmosphere, and other Physical Agents on the Condition of the Mind. Such Inquiries not only of scientific Interest, but also of practical Importance.- Physical Causes of Mental Illusions. - Examples of false Perceptions referred to the Sight and other Senses.—Other Forms of Illusion more frequent in Cases of Mental Aberration than mere Deceptions of the external Senses. -Mr. Locke's Definition of Insanity not sufficiently comprehensive. A too rapid Succession of Ideas, with Incapability of fixing the Attention, incompatible with correct Reasoning. - State of Mind in the socalled "Moral Insanity." - Question as to the Limits of Moral Responsibility.

THE conclusion of our journey had somewhat abruptly terminated our conversation. When we were assembled in the evening, the subject of it was thus resumed by Eubulus.

EUBULUS. Although some of the opinions which Ergates expressed this afternoon may be regarded as hypothetical, and not admitting of

actual and positive proof, yet it must be owned that they are supported by many facts, and by some in addition to those which he has himself adduced. Especially his views as to the nature of memory seem to afford an explanation of some circumstances, relating to the connection of the mind with the body, which cannot well be explained otherwise.

For instance: we remember nothing of what occurred in infancy. That part of our life seems afterwards to be a blank in our existence; and it is not unreasonable to suppose that the brain, like some other of the organs of the newly born child, is in an unfinished state, and, therefore, not fitted to retain the impressions made on it during any considerable period of time.

Then the impressions made on the memory gradually become fainter and fainter as time elapses; and this is in accordance with the gradual alteration which our physical structure undergoes as we advance in life. If there be exceptions to the rule, they are such as tend to prove the rule itself. For example, where the

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recollection of an event which occurred long ago is unusually vivid, we say "it seems as if it had happened only yesterday," and, on the other hand, when the recollection of an event which occurred only lately is unusually faint, it appears to us at first that it happened long ago; and it is only after some consideration, and by recalling to our mind some other circumstances in connection with it, that we are enabled to correct the error.

ERGATES. Allow me to interrupt you for a moment by observing that, besides those which I have already mentioned (namely, diseases and injuries of the brain), there are other physical agents which prevent the impression of things, of which we are conscious at the time, from being imprinted on the memory. Thus, a drunkard either forgets altogether, or has only a vague recollection of the nonsense which he talked, and the follies of which he was guilty, on the previous day while under the influence of alcohol; and those who, for the purpose of undergoing a surgical operation, are placed under the influence of what are called