In speaking of the brain, we often use words belonging to vision. Until the discovery of "concentrated light," we did not know how truthful were these expressions, one of which in our language answers to the "mind's eye." The eye as well as the brain contains concentrated light, and physical impressions received through the visual organs are by this electricity immediately conveyed to the sympathetic "light" of the brain. By the application of concentrated light we can even increase for a time the intellectual powers, or, rather, we can strengthen the instrument through which the intellectual powers are manifested. EXPERIMENT ON THE LIVING MAN. The possession of concentrated light led to the discovery of the exact mode in which the brain acts in the living man. By experiments on transparent fish of the zoophyte class, and on the eyes of animals, we discovered the means of making a living body for a time transparent. The skull was rendered transparent accordingly, and by the aid of concentrated light and of an instrument called an "electric viewer," the currents of electricity in the brain were made visible. These currents include myriads of electrical lines--literally composed of electricity--lines the nearest approach to your definition of a mathematical line, that which hath length without breadth. The filaments, as we may truly call them, are of different forms, straight, spiral, and otherwise curved, and of varied length and colours. They are set in motion by the impulsion of thought. When we talked to the patient on a particular subject, one series of lines would be set in motion with indescribable rapidity; other topics would call into play other series of straight or curved lines. They can also be set in motion under the influence of certain electricities. Although the experiments on the living man proved very valuable, they could not be conducted with impunity, and were therefore not often repeated. The man operated upon was insensible for some time afterwards, and felt the effects for years. He was, however, cared for during the rest of his life, and was not expected to work. Moreover, every kind of comfort, luxury, and amusement was provided for him and for a certain number of relatives and friends whom he selected as companions. Still he was not allowed to marry, that being one of the principal conditions to which he subscribed on being chosen for the experiment from amongst a host of candidates to whom all the serious consequences attending the operation were made known. XIV. PHYSICIANS. DISEASE GERMS. "Cure all evils in their early germ, so shall ye be spared endless suffering."