We at once place ourselves in difficulty in discussing this subject by the use of the words "conscious" and "consciousness," for, as so often happens, they are customarily applied in a vague and uncertain way to the mental activities of man--without any precise agreement as to what is meant by either of them. We are all agreed that a rational human being may go through a series of elaborate actions apparently directed by purpose and yet not be what we call "conscious," that is to say, "aware" of what he is doing. This occurs in "sleep-walking" and in "day-dreaming." And again, we know that a man may be evidently conscious during a certain period, and yet forget directly afterwards that he has been conscious and said and done certain things during that period. This often happens after "concussion of the brain." It is, as a matter of fact, uncertain whether one ought to regard the condition of a man during that obliterated or forgotten period of seeming consciousness as rightly to be described by the term "conscious." And the reason why one has this doubt is that we all recognize that consciousness without memory is really a contradiction in terms. Memory--the inscription or record in our brains of past experiences--exists without consciousness, as we all know, by observation of ourselves and our fellows. But the very essence of consciousness is memory. We cannot even be "conscious" of the experience of a single moment without being also conscious of the memory of some previous condition--however small, temporary, and incomplete the memory may be. To be conscious we must _compare_ the impressions reaching the brain at this moment with the memory of those of a past moment. And in lower animals and infants beginning to be conscious, the "recollections" available or accessible to consciousness may not extend farther back than a few seconds! If the memory of past experiences of which we are aware, that is to say, which are accessible to consciousness, is large and extends over the impressions of days, weeks, and years, then the conscious man or animal is in a totally different position from that of the man or animal who has only a very short and vague memory of which he or it is conscious. Thus it may be true that an animal or an infant is "conscious" and is comparing the present with the recollection of the past, and yet that the basis of comparison--the reach of memory accessible to consciousness--is so small as to be of little or no significance. Yet it is the beginning of a process which, gradually enlarging the access of consciousness to "memory," passes through a thousand degrees of increasing grasp and complexity (due to increased complexity in the microscopic connexions of the structural units, the branching nerve-corpuscles, which build up the brain) until it gives us the "consciousness" of a Shakespeare, a Newton, or a Darwin. The important fact in this consideration of what we mean by "conscious" and "consciousness" is, that memory is always for most lower animals, and during a period of growth in man, untouched by consciousness, and much of it remains so in all of us. As the dawn lights up a distant peak and then another and then a whole range and spreads to valley and plain, giving greater detail and variety as the moments pass--so does consciousness slowly invade in the course of development, whether of the individual or the species, the territory of memory. In the most man-like animals and the more ape-like men the process has not gone very far. In the highest apes consciousness is so limited in its access to memory that it is but a glimmer, a mere rudiment, of what it becomes in the modern races of mankind. We must not overlook the fact that it is only when we have to deal with men far advanced from the state of primeval savagery that the memory itself becomes rich and varied. Observation, memory, and record--the vast tradition of taboo, knowledge, custom, law, and religion not inborn in our structure but handed on by spoken or written word--are developed and increased by the very fact that the daylight of consciousness has reached the memory of them when less copious than they become in later development, and has given them life-saving value.