in this sense only, meaning that the memory of it is not permanently lost but that under certain particular circumstances we can recall it. Now a large mass of observations demonstrate that there are an enormous number of experiences, belonging to both normal and abnormal mental life, which we are unable to voluntarily recall during any period of our lives, no matter how hard we try, or what aids to memory we employ. For these experiences there is life-long amnesia. Nevertheless, it is easy to demonstrate that, though the personal consciousness of everyday life cannot recall them, they are not lost, properly speaking, but conserved; for when the personal consciousness has undergone a peculiar change, at moments when certain special alterations have taken place in the conditions of the personal consciousness, at such moments you find that the subject under investigation recalls the apparently lost experiences. These moments are those of hypnosis, abstraction, dreams, and certain pathological states. Again, in certain individuals it is possible by technical devices to awaken secondary mental processes in the form of a subconsciousness which may manifest the memories of the forgotten experiences without awareness therefor on the part of the personal consciousness. These manifestations are known as automatic writing and speech. Then, again, by means of certain post-hypnotic phenomena, it is easy to study conservation experimentally. We can make, as you will later see, substantially everything that happened to the subject of the experiment in hypnosis—his thoughts, his speech, his actions, for all of which he has complete and irretrievable loss of memory in a waking state—we can make memory for all these lost experiences reappear when hypnosis is again induced. Thus we can prove conservation when voluntary memory for experiences is absolutely lost. These experiments, among others, as we shall also see, also give an insight into the nature of conservation which is the real problem involved in an investigation into the process of memory. Before undertaking to solve this problem—so far as may be done—it is well to obtain a full realization of the extent to which experiences which have been forgotten may be still conserved. I will therefore, as I promised you, résumé the experimental and other evidence supporting this principle, making use of both personal observations and those of others. _NOTE—In the following exposition of the evidence for the theory of memory it has been necessary to make use of phenomena subsuming subconscious processes before the subconscious itself has been demonstrated. A few words in explanation of the terms used is therefore desirable to avoid confusing the reader._