He knew the necessity of the nerve supply to the muscle, and that the brain originated the consequent motion of a muscle so supplied, and proved the fact experimentally by cutting through some of the nerves and so paralysing the part.[501] Where the origin of the nerve is, there, he said, it is admitted by all physicians and philosophers is the seat of the soul. This, he adds, is in the brain and not in the heart. The principles of voluntary motion were well understood, therefore, by Galen, and he must have possessed “clear mechanical views of what the tensions of collections of strings could do, and an exact practical acquaintance with the muscular cordage which exists in the animal frame:—in short, in this as in other instances of real advance in science, there must have been clear ideas and real facts, unity of thought and extent of observation, brought into contact.”[502] He observed that although a ligature on the inguinal or axillary artery causes the pulse to cease in the leg or in the arm, the operation is not permanently injurious, and that even the carotid arteries may be tied with impunity. He corrects the error of those who, in tying the carotids, omitted to separate the contiguous nerves, and then wrongly concluded that the consequent loss of voice was due to compression of the arteries. Galen was the first and greatest authority on the pulse, if not our sole authority; for all subsequent writers simply transferred his teaching on this subject bodily to their own works.[503] Briefly it was as follows: “The pulse consists of four parts, of a diastole and a systole, with two intervals of rest, one after the diastole before the systole, the other after the systole before the diastole.”[504] His therapeutics were based on these two principles:—“1. That disease is something contrary to nature, and is to be overcome by that which is contrary to the disease itself; and 2. That nature is to be preserved by that which has relation with nature.”[505] The affection contrary to nature must be overcome, and the strength of the body has to be preserved. But while the _cause_ of the disease continues to operate, we must endeavour to remove it; we are not to treat symptoms merely, for they will disappear when their cause is removed, and we must consider the constitution and condition of the patient before we proceed to treat him. “Such as are essentially of a good constitution are such in whose bodies heat, coldness, dryness, and moisture are equally tempered; the instruments of the body are composed in every part of due bigness, number, place, and formation.”[506] He gives in succeeding chapters the signs of a hot, cold, dry, moist, hot and dry, hot and moist, cold and dry, and cold and moist brain; of a heart overheated, of a heart too cold, of a dry and of a moist heart, of a heart hot and dry, hot and moist, cold and moist, cold and dry heart. The liver is described under the same conditions.