The first and one of the most important questions to be determined in dealing with the subject of insanity is the meaning which we ought to attach to the word insanity itself. The condition which the word is supposed to indicate has most important relations, both social and scientific. It is a frequent subject of popular discussion, and it forms an important element in many enquiries—philosophical, medical, and juridical. Speaking generally, it may be said that it invariably signifies a marked abnormality of mental condition. But it is frequently necessary that we should be able to form a much more precise idea of the degree as well as the kind of abnormality that it implies. And a very superficial examination is sufficient to show that the degree and the kind vary greatly, according to the point of view from which the subject is regarded.