574 THE POPULAR SCIENCE MONTHLY 



veloped a line of theoretical reasoning to its fullest and, by watching 

 his experimental evidence, could grasp whatever facts showed them- 

 selves 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 lab- 

 oratory. 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 look- 

 ing 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 Miiller, 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 en- 

 tirely 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 cir- 

 culation must be governed by nerves not subject to the will, but influ- 

 enced 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 sym- 

 pathetic 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: 



