By a further study of the symptoms and of the course of mental diseases, psychiatrists ultimately became able to diagnose mental derangements at a time at which ordinary people would have been able to perceive little or no alteration of the mental processes of the patients. All this rests solely on experience. Only through experience has it come to pass that we can now, on recognizing a certain set of symptoms, predict a certain course of the psychical process.

Should our experiences in the department of psychiatry receive an augmentation, we shall have every reason to be thankful; for, in, spite of all our efforts, we stand upon the threshold of the science. But every new experience brings new difficulties with it, for it is from experience that we have to draw our conclusions. Now, new experiences often wreck our finest theories, in one or other of two ways— namely, first, by not confirming them, or, secondly, by conflicting with them. That is the way with unprejudiced tests and objective judgments.

Accordingly, after a great number of mental maladies, such as paranoia, progressive paralysis, certain forms of melancholia, mania, etc., had been found to be accompanied by hallucinations as an important symptom, the discovery was made that a great number of famous men—the so-called men of genius—were equally subject to deceptions of the senses. What does that show? Does it show that those men were insane? Such is the inference drawn by Moreau and Lombroso. But is it logical? Why not rather conclude that hallucination is not such an unfavourable symptom as we had supposed?

Moreau and Lombroso take it for granted that hallucinations only occur in mental disease. How do they prove that? Do not the very facts they adduce, if they be facts, disprove it?

We find a man full of crazy notions, with his self-consciousness gone, or with general loss of intelligence; and we mark him as unquestionably insane, and proceed to study the phenomena of his mind as symptoms of insanity. We meet another man whose achievements are positively great, who has, all his life long, excited the admiration and astonishment of his fellows, and who behaves in the most complete consciousness of what he is about. Ought we not to reckon him as sane beyond a doubt, and take his psychological processes as the very type of purely healthy phenomena?