and one

which there is in man of any original or intuitive connection between the ideas formed through visual and through tactile sensations. He was well acquainted with a dog or cat by feeling, but could not remember their respective characters when he saw them; day, when thus puzzled, he took up the cat in his arms, and felt her attentively, so as to associate the two sets of cognitions, and then, setting her down, said, 'So, puss, I shall know you another time."

Another very excellent example is recorded by Critchett in the 6 Medico-Chirurgical Transactions,' vol. xxxviii., of a young woman who had been blind from her birth, but had obtained her sight by an operation:

'I found,' says the operator, 'that she was never able to ascertain what an object really was by sight alone, although she could correctly describe its shape and colour; but that after she had once instructed one sense through the medium of the other, and compared the impressions conveyed by touch and sight, she was ever after able to recognise the object without touching it. In this respect her memory was very perfect; I never knew her fail in a single instance, though I put this power frequently to the test of experiment. It was curious to place before her some very familiar object that she had never compared in this way, such as a pair of scissors. She would describe their shape, colour, glistening metallic character, but would fail in ascertaining what they really were until she put a finger on them, when in an instant she would name them, and laugh at her own stupidity, as she called it, in not having made them out before.'

So the remembrance of an impression is in accord

ance with that impression; thus when an afferent impression has been received in the centre for sensory memory, it produces such a modification of the protoplasm of the ganglion cells there, as to allow the complete impression to be brought before the consciousness, when the attention is brought to bear upon the subject. This modification of the protoplasm is permanent, only varying in intensity with time, and constitutes the sensory memory. This diminution in the intensity of the impression is well exemplified in the following way. If a person of average ability, directly after having looked at a picture or a photograph, close his eyes and think of the picture, the remembrance of it will be almost as vivid as the sensory impression itself; if the observer had waited for a minute or two before trying to think of the picture, the remembrance would have been less vivid; in a day feeble, in a week of still less intensity, the remembrance varying with individuals, some being able to have a fair remembrance of the picture, others failing to have the slightest recollection of it.

But, besides the memory of external impressions, there is the memory of internal impressions, that is, the remembrance of thoughts, perceptions, and the other processes of the mind. Thus, when looking at the picture, various ideas usually occur to the observer, and when thinking of it again he remembers these ideas. Every idea and thought which occurs to the mind, depends primarily upon some external influence, however much it may be altered from the original. This forms an important class of impressions, only differing in this, that instead of being received and elaborated by the sensory nerves and their centres, and conducted

upwards to the centres for sensory memory, they are originated by the higher parts of the brain, and conducted downwards to the centre.

Thus, there are two divisions of sensory memory :

1. That memory which consists of the modification of the protoplasm of the cells of the centre, produced by sensory impressions as received.

2. That memory which consists of the modification of the protoplasm of the cells of the centre, produced by impressions of thoughts and ideas based on sensorial impressions.

Our knowledge of the external world is all based on impressions conveyed to the brain by the sensory nerves, which convey a larger number of impressions than are included under the names of the special senses, sight, hearing, smell, touch, and taste; thus, we also receive impressions of the condition of the muscles, temperature, visceral and pathological sensations.

No impression which has ever been brought before the mind, whether originated by any object in the external world, or by the action of any of the faculties, is ever entirely lost.

This necessarily follows, assuming the process of memory described above to be true, namely, that memory consists of the modification of the protoplasm of the receptive cells produced by an impression, the intensity of the modification only diminishing with time. The change in the protoplasm which constitutes memory can only take place in cells having an original construction fitted for the purpose, in the same way as only the cells of the retina can respond to light. All cells undergo modifications when submitted to certain influencing conditions; but these modifications do not

constitute memory, neither does that increased functional activity which results from stimulation when not excessive.

As an impression must reach a certain sum of intensity before it is brought before the consciousness, the greater number of impressions never become revived, because this intensity is not attained. They remain in a latent condition, waiting for an appropriate stimulus for their revival to take place. How often the most trivial incidents are brought back, by some strong resemblance or association-events and details so far forgotten, that if narrated by others, they would not have been recognised as having occurred.

There are very few persons, excepting perhaps the most feeble-minded individuals, who are not able to recognise an anecdote when told with all its details by another a second time, at a comparatively short period after the first recital, though they might not have been able to repeat it correctly themselves. If the original modification of the protoplasm caused by the anecdote had disappeared, then no stimulus, however strong, would be able to bring it back to the mind. It is very rare for a person not to remember an occurrence if he be placed in exactly the same circumstances as when he received the original impression.

The following are instances of the revival of old impressions. Numerous cases might be given, as examples of this class are very common :

1. Several years ago, the Rev. S. Hansard, now rector of Bethnal Green, was doing clerical duty for a time at Hurstmonceaux, in Sussex; and while there he one day went over with a party of friends to Pevensey Castle, which he did not remember to have ever pre

viously visited. As he approached the gateway, he became conscious of a very vivid impression of having seen it before; and he seemed to himself to see not only the gateway itself, but donkeys beneath the arch, and people on top of it. His conviction that he must have visited the Castle on some former occasion--although he had not the slightest remembrance of such a visit, nor any knowledge of having been in the neighbourhood previously to his residence at Hurstmonceaux— made him inquire from his mother if she could throw any light on the matter. She at once informed him that, being in that part of the country when he was about eighteen months old, she had gone over with a large party, and had taken him in the pannier of a donkey; that the elders of the party having brought lunch with them, had eaten it on the roof of the gateway, where they would have been seen from below; whilst he had been left on the ground with the attendants and donkeys. This case is remarkable for the vividness of the sensorial impression (it may be worth while to notice that Mr. Hansard has a decidedly artistic temperament) and for the reproduction of details which were not likely to have been brought up in conversation, even if he had happened to hear the visit itself mentioned as an event of his childhood, and of such mention he has no remembrance whatever.'— CARPENTER: Mental Physiology.'

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2. A lady in the last stage of chronic disease was carried from London to a house in the country; there her infant daughter was taken to visit her, and after a short interview carried back to town. The lady died a few days after, and the daughter grew up without any recollection of her mother till she was of mature age.