[51] If the old man preserves with difficulty the memory of the most recent events, whilst he often retraces with the greatest ease the recollection of the most distant ones, it is not because the first have been more faithfully transmitted to him by his senses, but because these events had produced a greater impression on him. This is so true, that failure of the memory is sometimes remarked in old people who have their senses in perfection. On the other hand, very imperfect sensations may produce a very lively impression. A connoisseur in painting, when his sight is very bad, experiences in seeing a beautiful picture, a hundred times more pleasure, than one who is indifferent to it, though he examines it with good eyes, and the connoisseur preserves the image of it long after the other has lost it. We do not perceive the recollection of things, unless there is some circumstance connected with them that makes a lively impression; but in the same event, this circumstance will not be the same in all individuals, and it is sometimes by the most trifling of all that a man fixes the fact in his memory. [52] This failure of the senses appears in animals as well as man, and it may be observed in those whom we suffer to grow old among us. We often see dogs becoming blind and deaf; and these infirmities are perhaps more common in them than in man. But as these animals are rarely permitted to arrive at extreme old age, we have not often an opportunity of observing them. [53] By defending the skin from the shock of external bodies, and by preserving it from the variation of temperature, dress very certainly preserves its sensibility, and far from impairing the sense of touch, as Bichat maintains, it acts as a circumstance favourable to its preservation. [54] The animal no doubt does not tremble at the moment of death; for he does not see it. His present sensation is every thing to him. If he suffers at the approach of death, he shows it by the usual signs; but it is only the present pain that he expresses, he sees nothing beyond. The child is in this respect, in the same situation as the animal. [55] In order to ascertain the cause of the differences in the cooling of the body after the various kinds of death, it is necessary to examine what general conditions can have an influence in the cooling of a body left to itself. Of these there are three principal ones. Under the same external circumstances, a body will cool so much the slower. 1st. As its temperature at the beginning of the experiment, shall be higher in relation to that of surrounding bodies; 2d. As its surface shall be less in relation to its size; 3d. And as its exterior parts shall be less perfect conductors of heat.