August 30, 1912] 



SCIENCE 



265 



ethanol) . Here we have literally the material- 

 ization of a chemical idea, the crystallization 

 of a notion ; the thing of the mind has become 

 a thing of the laboratory, the thought has been 

 captured and bottled. 



The next " as it were " we shall take from 

 the history of the physiology of the central 

 nervous system in the writings of a pupil of 

 Harvey, Dr. Thomas Willis. At the present 

 day the name and the process " reflex action " 

 is as well established as is anything in animal 

 behavior. One of the most certain things in 

 the physiology of the nervous system is that if 

 we stimulate a nerve going into it, we shall 

 produce outgoing effects, muscular contrac- 

 tions, vascular or glandular changes. If we 

 decapitate a frog and hang up the body and 

 apply a piece of acid paper to one flank, the 

 leg of that side will be brought up to flick it 

 off, and if the acid be very strong the whole 

 frog will be thrown into convulsions — ^these 

 movements are reflex actions. Now this very 

 definite physiological conception of a reflex 

 neural action arose in a metaphor, in an " as 

 it were " of Willis penned about 1650. He 

 said : 



We may admit that the impression of an object 

 driving the animal spirits inwards and modifying 

 them in a certain peculiar manner, gives rise to 

 sensation and that the same animal spirits, in that 

 they rebound from within outwards in a reflected 

 wave as it were, call forth local movements. 



Willis's notion was that of a wave reflected 

 back towards its source, but the metaphor 

 about nerve impulses being reflected evidently 

 represented the truth, for it has lived on and 

 become an integral part of the terminology of 

 neural activity. K there had been no germ of 

 accurate description in it, the idea contained 

 in the metaphorical phrase " as it were re- 

 flected," would not have survived to our own 

 day; but it has lived to become the definite 

 description of a fundamental neural truth. 



Dr. Marshall Hall, who did so much for the 

 physiology of this sort of action, adopted the 

 phrase and incorporated it in one of his own — 

 the " reflex nerve-arc " which denotes the 

 anatomical path over which reflected nerve- 

 impulses travel. If Willis could visit our 



laboratories to-day, we could show him reflex 

 actions performed with automatic precision, 

 and below the microscope we could let him see 

 the various links in a reflex nerve-arc. He 

 would find his " as it were reflected " no longer 

 taken in a metaphorical sense, but used as the 

 most appropriate mode of denoting one of the 

 commonest and most important of neural 

 activities. 



The study of nerve-impulses gives us an- 

 other example of the inevitable tendency to- 

 wards concreteness and definiteness in notions 

 regarding the behavior of the central nervous 

 system. If we go sufficiently far back, we find 

 the Greeks, for instance, imagining that the 

 nerve fibers conveyed spirits through their 

 pores (poroi). No doubt these spirits of 

 antiquity are the synonym of our " nerve- 

 impulses," something propagated with con- 

 siderable rapidity from one end of a nerve to 

 the other. Still for ages that something was 

 quite unapproachable on the part of the senses. 

 Some physiologists imagined that the muscles 

 became active because the spirits of the nerves 

 rushed into them, but Borelli (1670) on cut- 

 ting open living muscles under water could see 

 no bubbling of gas or anything else suggesting 

 them to be inflated with any kind of substance 

 — spirit, flatus, succus nerveus or gas. But it 

 is to his credit that Borelli looked for some- 

 thing of the kind; he desired to render the 

 succus nerveus concrete, to see the action of 

 the spirits in the nerves, if possible. It was 

 not to be; for nerve-impulses are a mode of 

 motion and only to be discovered through their 

 effects. In our ovm day, one evidence of their 

 passage along nerves, namely, the electrical, 

 has been made sufficiently obvious by that 

 exquisite instrument the galvanometer. By 

 the aid of this very delicate apparatus, the 

 electric currents produced by the nerve im- 

 pulses can be made to swing a mirror reflect- 

 ing a beam of light on to a screen, it may be, 

 several feet away. Although nerve-impulses 

 are no more visible to-day than were the nerve 

 spirits of the Greeks or was the succus nerveus 

 of Borelli, we are in a position to show these 

 thinkers of the past a spot of light jerked two 

 or three feet to the right or left of its resting 



