A mind that surrenders itself to a single idea becomes essentially insane. I know a man who has dwelt so long upon the subject of a vegetable diet that it has finally taken possession of him. It is now of such importance in his eyes that every other subject is thrown out of its legitimate relations to him. It is the constant theme of his thought--the study of his life. He questions the properties and quantities of every mouthful that passes his lips, and watches its effects upon him. He reads upon this subject everything he can lay his hands on. He talks upon it with every man he meets. He has ransacked the whole Bible for support to his theories; and the man really believes that the eternal salvation of the human race hinges upon a change of diet. It has become a standard by which to decide the validity of all other truth. If he did not believe that the Bible was on his side of the question, he would discard the Bible. Experiments or opinions that make against his faith are either contemptuously rejected or ingeniously explained away. Now this man's mind is not only reduced to the size of his idea, and assimilated to its character, but it has lost its soundness. His reason is disordered. His judgment is perverted--depraved. He sees things in unjust and illegitimate relations. The subject that absorbs him has grown out of proper proportions, and all other subjects have shrunk away from it. I know another man--a man of fine powers--who is just as much absorbed by the subject of ventilation; and though both of these men are regarded by the community as of sound mind, I think they are demonstrably insane.