veloped a line of theoretical reasoning to its fullest and, by watching his experimental evidence, could grasp whatever facts showed themselves unbiased by the reasoning which had suggested the experiment. He emphasized imagination and preconceived theory when used in their proper places and used to say:
Put off your imagination as you take off your overcoat when you enter the laboratory; but put it on again, as you do the overcoat, when you leave the laboratory. Before the experiment and between whiles let your imagination wrap you round; put it right away from yourself during the experiment itself, lest it hinder your observing power.
His discovery of the vasomotor nerves was hardly less important than the discovery of glycogen. These nerves control the circulation of the blood by causing the muscles in the walls of the blood vessels to increase or diminish the bore thus allowing more or less blood to flow through at one time. The nerves belong to the sympathetic system, that is, they are not under the control of the will but stimulated by sensory impulses. The part played by him in this work was different, for he did not realize the importance of his discovery. As usual, he was looking for something else, and did not immediately turn aside to follow the new line of work.
The knowledge of the blood vessels at this time was very limited and inexact. Johannes Müller, the foremost physiologist in Germany, in his classical work on physiology in 1838, concluded that the arteries did not possess a muscular coat but only physical elasticity. He was entirely unprepared for the idea of vasomotor nerves. The sympathetic nerves had been traced to the blood vessels and some thought they should have something to do with the circulation. Stilling introduced the word "vasomotor" in arguing from theoretical grounds that the circulation must be governed by nerves not subject to the will, but influenced by sensory stimuli. In 1846, Kolliker discovered that plain muscle was made up of minute spindle-shaped cells either in clumps or scattered. This cleared up the doubts concerning the muscle coat of the blood vessels. The way was now open for the proof of the vasomotor nerves, but no one saw it.
Bernard proposed to study the influence of the nerves on animal heat, and began by attempting to ascertain the effect of cutting a sympathetic nerve on the temperature of that part of the body affected by it. He conceived that the action of the nerve, if any, would be in governing the chemical changes involved in heat production, and expected to find a section of the nerve would cause a lowering of temperature. Working on the cervical sympathetic nerve in a rabbit, he was astonished to find an increase instead of a diminution in heat on the side of the head where the section was made. He reported:
