To take one other example as illustrating a somewhat different aspect of this question. An experienced physician arrives in a moment at the diagnosis of a case presented to his notice, but a well read and well informed student may ponder long before attaining a correct conclusion under exactly similar circumstances. In what does the difference between the mental processes in the two individuals consist? It will be said to be a matter of experience merely; but what does this statement imply? In the process of arriving at a diagnosis of the case many facts will have to be observed, many points criticised, and many arguments weighed and valued. Now in the case of the senior observer all these facts, these points, these arguments will perhaps have been passed through the mind some hundreds of times before, in reviewing similar cases; the various steps whereby his final opinion is attained will, by frequent exercise and repetition, have become separately organised in the brain, and, however rapidly his conclusion may have been arrived at, the various steps will have been undertaken. But inasmuch as their influence is exercised automatically, he remains unconscious of their agency, until he stops to analyse the various reasons that have—to a very great extent unconsciously—laid the foundations of his diagnosis and the various details on which his opinion has been founded. The process may involve no more consciousness than is displayed in the movements of the envelope folder; one is aware that the envelope is folded, and the other that he has arrived at a definite opinion; but neither may be awake to the separate steps of the process until they deliberately investigate the details of the preceding movements. In the case of the immature observer, frequent repetition has not as yet made certain processes necessary to the diagnosis of the case familiar to his mind, and in consequence they have attained no sound structural position in his nerve centres; so, like the novice in the mystery of envelope folding, he has to consider each step, and proceed with deliberation, and under the acute guardianship of consciousness.