This curious property which sensorial impressions received at the same time possess, and which consti tutes as it were natural families among them, is a great resource in the education of the intellect, and the methodic cultivation of its faculties. When a series of memories, a series of ideas, of experimental facts and scientific principles, has been imprinted on it, it admits of their being artificially evoked, contenting itself with an appeal to the first in the series of memories, which is in a manner at the head of the line.
Thanks to this connection between our particular reminiscences, the intelligence incessantly acquires new riches, and may at a given moment, by means of its automatic activity, seize upon these riches and make use of them.
Thus, when from observation of a clinical fact, for instance, we have learned that, a case of acute rheu matic arthritis being given, this condition of effusion into the joints is accompanied by a similar manifes tation as regards the heart, these two impressions hence forward form in the mind two united memories ; so that, the first being given, the second immediately arises, and vice versa. In the presence of a patient with rheuma tism we think of a cardiac affection, and conversely in the presence of an old affection of the heart, we interrogate the patient as to his rheumatismal ante cedents.
When I have learnt from the experience of my masters that lesions of the posterior roots and posterior columns of the cord are accompanied by defective co-ordination of movements, ocular disturbances, sharp sudden pains in the limbs, gastric troubles, etc., I have anastomosed in my mind by study a series of memories associated one with another and forming a sort of federation ; so that when one happens to be isolatedly evoked—when, for instance, 1 see a patient with special ocular troubles, I spontane ously think of defective co-ordination of his movements, the existence of sharp sudden pains, etc.
What here takes place in an order of facts clearly determined, with regard to a series of phenomena methodically regulated, is constantly and regularly renewed in us during the period of our daily acti vity.
When every region of our brain is in erethism, we all know how memories appeal one to another ; always following' the same series in their method of appearing, without our being able to command them. It is sufficient to see an object or a person—to hear a name pronounced accidentally, to smell an odour—in order to feel arising within us a series of ideas which arose at the moment when this impression was at first perceived by us. We all know how frequently in current conversation a word—a simple sound—causes the primi tive direction of our ideas to diverge. Many persons indeed thus lose sight of the point of departure, acci dentally led away by a passing reminiscence which introduces divergent thoughts, and insensibly causes them to turn aside from the subject with which they have started.
Do we not all know that when we wish at a given moment to evoke a particular reminiscence, and fear that the distractions of our current life will cause us to forget it, we mentally attach the object to some sign, which thus becomes for us the clue that recalls it to our mind. Every one has his own mnemonic on such occasions, and we all know that it is sometimes a knot made on a pocket-handkerchief— an object which must necessarily pass through our hands, a ribbon fixed upon our garments, a visible mark designed to catch our eye mechanically, to which we have recourse, in order to cause the reminiscence we wish to evoke to leap forth in the natural course of events.*