84 



LECTURES AND ESS A YS 



losing themselves in the muscles. Those 

 filaments or cords are the nerves, which 

 you know are divided into two kinds, 

 sensor and motor, or, if you like the 

 terms better, afferent and efferent nerves. 

 The former carry impressions from the 

 external world to the brain; the latter 

 convey the behests of the brain to the 

 muscles. Here, as elsewhere, we find 

 ourselves aided by the sagacity of Mayer, 

 who was the first clearly to formulate the 

 part played by the nerves in the organism. 

 Mayer saw that neither nerves nor brain, 

 nor both together, possessed the energy 

 necessary to animal motion ; but he also 

 saw that the nerve could lift a latch and 

 open a door, by which floods of energy 

 are let loose. " As an engineer," he 

 says with admirable lucidity, " by the 

 motion of his finger in opening a valve 

 or loosening a detent, can liberate an 

 amount of mechanical energy almost 

 infinite compared with its exciting cause; 

 so the nerves, acting on the muscles, can 

 unlock an amount of power out of all 

 proportion to the work done by the 

 nerves themselves." The nerves, accord- 

 ing to Mayer, pull the trigger, but the 

 gunpowder which they ignite is stored in 

 the muscles. This is the view now 

 universally entertained. 



The quickness of thought has passed 

 into a proverb, and the notion that any 

 measurable time elapsed between the 

 infliction of a wound and the feeling of 

 the injury would have been rejected as 

 preposterous thirty years ago. Nervous 

 impressions, notwithstanding the results 

 of Haller, were thought to be transmitted, 

 if not instantaneously, at all events with 

 the rapidity of electricity. Hence, when 

 Helmholtz, in 1851, affirmed, as the 

 result of experiment, nervous transmis- 

 sion to be a comparatively sluggish 

 process, very few believed him. His 

 experiments may now be made in the 

 lecture-room. Sound in air moves at 

 the rate of 1,100 feet a second; sound 

 in water moves at the rate of 5,000 feet 

 a second ; light in ether moves at the 

 rate of 186,000 miles a second, and elec- 

 tricity in free wires moves probably at the 



same rate. But the nerves transmit 

 their messages at the rate of only 70 feet 

 a second, a progress which in these 

 quick times might well be regarded as 

 inordinately slow. 



Your townsman, Mr. Gore, has pro- 

 duced by electrolysis a kind of antimony 

 which exhibits an action strikingly analo- 

 gous to that of nervous propagation. A 

 rod of this antimony is in such a mole- 

 cular condition that when you scratch or 

 heat one end of the rod the disturbance 

 propagates itself before your eyes to the 

 other end, the onward march of the dis- 

 turbance being announced by the develop- 

 ment of heat and fumes along the line of 

 propagation. In some such way the 

 molecules of the nerves are successively 

 overthrown ; and if Mr. Gore could only 

 devise some means of winding up his 

 exhausted antimony, as the nutritive 

 blood winds up exhausted nerves, the 

 comparison would be complete. The 

 subject may be summed up, as Du Bois- 

 Reymond has summed it up, by reference 

 to the case of a whale struck by a harpoon 

 in the tail. If the animal were seventy 

 feet long, a second would elapse before 

 the disturbance could reach the brain. 

 But the impression after its arrival has 

 to diffuse itself and throw the brain into 

 the molecular condition necessary to 

 consciousness. Then, and not till then, 

 the command to the tail to defend itself 

 is shot through the motor nerves. 

 Another second must elapse before the 

 command can reach the tail, so that 

 more than two seconds transpire between 

 the infliction of the wound and the 

 muscular response of the part vrounded. 

 The interval required for the kindling of 

 consciousness would probably more than 

 suffice for the destruction of the brain by 

 lightning, or even by a rifle-bullet. Before 

 the organ can arrange itself it may, there- 

 fore, be destroyed, and in such a case we 

 may safely conclude that death is pain- 

 less. 



The experiences of common life supply 

 us with copious instances of the libera- 

 tion of vast stores of muscular power 



