470 



NA TURE 



[September 14, 1893 



ing it as merely a part of the great science of life) has hitherto 

 followed, and why physiologists have been unwilling to enter 

 on it. The study of the less complicated internal relations of 

 the organism has afforded so many difficult problems that the 

 most difficult of all have been deferred ; so that although the 

 psycho-physical method was initiated by E. H. Weber in the 

 middle of the present century, by investigations ' which formed 

 part of the work done at that epoch of discovery, and although 

 Prof. Wundt, also a physiologist, has taken a larger share in 

 the more recent development of the new study, it is chiefly by 

 psychologists that the researches which have given to it its 

 importance as a new discipline have been conducted. 



Although, therefore, experimental psychology has derived its 

 methods from physical science, the result has been not so much 

 that physiologists have become philosophers, as that philoso- 

 phers have become experimental psychologists. In our own 

 universities, in those of America, and still more in those of 

 Germany, psychological students of mature age are to be found 

 who are willing to place themselves in the dissecting-room side 

 by side with beginners in anatomy, in order to acquire that 

 exact knowledge of the framework of the organism without 

 which no man can understand its working. Those, therefore, 

 who are apprehensive lest the regions of mind should be in- 

 vaded by the insaniens sapienlia ol the laboratory, may, I think, 

 console themselves with the thought that the invaders are for 

 the most part men who before they became laboratory workers 

 had already given their allegiance to philosophy ; their purpose 

 being not to relinquish definitively, but merely to lay aside for 

 a time, the weapons in the use ot which they had been trained, 

 in order to learn the use of ours. The mo'-ive that has encour- 

 aged them has not been any hope of finding an experimental 

 solution of any of the ultimate problems of philosophy, but the 

 conviction that, inasmuch as the relation between mental stimuli 

 and the mental processes which they awaken is of the same 

 order with the relation between every other vital process and its 

 specific determinant, the only hope of ascertaining its nature 

 must lie in the employment of the same methods of comparative 

 measurement which the biologist uses for similar purposes. Not 

 that there is necessarily anything scientific in mere measurement, 

 but that measurement affords the only means by which it can be 

 determined whether or not the same conformity in the relation 

 between stimulus and reaction which we have accepted as the 

 fundamental characteristic of life, is also to be found in mind, 

 notwithstanding that mental processes have no known physical 

 concomitants. The results of experimental psychology tend to 

 show that it is so, and consequently that in so far the processes 

 in question are as truly functions of organism as the contraction 

 of a muscle, or as the changes produced in the retinal pigment 

 by light. 



I will make no attempt even to enumerate the special lines of 

 inquiry which during the last decade have been conducted with 

 such vigour in all parts of the world, all of them traceable to 

 the influence of the Leipzig school ; but will content myself 

 with saying that the general purpose of these investigations 

 has been to determine with the utmost attainable precision the 

 nature of psychical relations. Some of these investigations 

 begin with those simpler reactions which more or less resemble 

 those of an automatic mechanism, proceeding to those in which 

 the resulting action or movement is modified by the influence of 

 auxiliary or antagonistic conditions, or changed by the simul- 

 taneous or antecedent action on the reagent of other stimuli, in 

 all of which cases the effect can be expressed quantitatively ; 

 others lead to results which do not so readily admit of measure- 

 ment. In pursuing this course of inquiry the physiologist finds 

 himself as he proceeds more and more the coadjutor of the 

 psychologist, less and less his director ; for whatever advantage 

 the former may have in the mere technique of observation, the 

 things with which he has to do are revealed only to introspec- 

 tion, and can be studied only by methods which lie outside of 

 his sphere. I might in illustration of this refer to many recent 

 experimental researches — such, for example, as those by which 

 it his been sought to obtain exact data as to the physiological 

 c >ncomitants of pleasure and of pain, or as to the influence of 

 weariness and recuperation, as modifiers of psychological re- 

 actions. Another outwork of the mental citadel which has 

 been invaded by the experimental method is that of memory. 

 Even here it can be shown that in the comparison of transitory 

 as compared with permanent memory — as, for example, in the 



1 Weber's researches were published in Wagner's Haruhi'orterlmch, I 

 hink, in 1849. 



getting off by heart of a wholly uninteresting series of words, 

 with subsequent oblivion and reacquisition — the labour of 

 acquiring and reacquiring may be measured, and consequently 

 the relation between them ; and that this ratio varies according 

 to a simple numerical law. 



I think it not unlikely that the only effect of what I have said 

 may be to suggest to some of my hearers the question. What is 

 the use of such inquiries? Experimental psychology has, to the 

 best of my knowledge, no technical application. The only 

 satisfactory answer I can give is that it has exercised, and will 

 exercise in future, a helpful influence on the science of life. 

 Every science of observation, and each branch of it, derives 

 from the peculiarities of its methods certain tendencies which 

 are apt to predominate unduly. We speak of this as specialis- 

 ation, and a''e constantly striving to resist its influence. The 

 most successful way of doing so is by availing ourselves of the 

 counteracting influence which two opposite tendencies mutually 

 exercise when they are simultaneous. He that is skilled in the 

 methods of introspection naturally (if I may be permitted to say 

 so) looks at the same thing from an opposite point of view to 

 that of the experimentalist. It is, therefore, good that the two 

 should so work together that the tendency of the experiment- 

 alist to imagine the existence of mechanism where none is 

 proved to exist— of the psychologist to approach the phenomena 

 of mind too exclusively from the subjective side — may mutually 

 correct and assist each other. 



Photolaxis and Chemiotaxis. 



Considering that every organism must have sprung from a 

 unicellular ancestor, some have thought that unless we are pre- 

 pared to admit a deferred epigenesis of mind, we must look for 

 psychical manife^tations even among the lowest animals, and 

 that as in the protozoon all the vital activities are blended 

 together, mind should be present among them not merely 

 potentially but actually, though in diminished degree. 



.Such a hypothesis involves ultimate questions which it is 

 unnecessary to enter upon : it will, however, be of interest in 

 connection with our present subject to discuss the phenoraeua 

 which served as a basis for it — those which relate to what may 

 be termed the behaviour of unicellular organisms and of indi- 

 vidual cells, in so far as these last are capable of reacting to 

 external influences. The observations which afford ns most 

 information ate those in which the stimuli employed can be 

 easily measured, such as electrical currents, light, or chemical 

 agents in solution. 



A single instance, or at most two, must suffice to illustrate the 

 influence of light in directing the movements of freely moving 

 cells, or, as it is termed, phototaxis. The rod-like purple 

 organism called by Engelmann Bacterium photometncum,\ is 

 such a light-lover that if you place a drop of water containing 

 these organisms under the microscope, and focus the smallest 

 possible beam of light on a particular spot in the field, the spot 

 acts as a light trap and becomes so crowded with the little rod- 

 lets as to acquire a deep port-wine colour. If instead of makiivg 

 his trap of white light, he projected on the field a microscopic 

 spectrum, Engelmann found that the rodlets showed their pre- 

 ference for a spectral colour, which is absorbed when trans- 

 mitted through their bodies. By the aid of a light trap of the 

 same kind, the very well-known spindle-shaped and flagellate 

 cell of Euglena can be shown to have a similar power of dis- 

 criminating colour, but its preference is different. This familiar 

 organism advances with its flagellum forwards, the sharp end of 

 the spindle having a red or orange eye point. Accordingly, 

 the light it loves is again that which is most absorbed — viz., 

 the blue of the spectrum (line F). . 



These examples may serve as an introduction to a similar 

 one in which the directing cause of movement is not physical 

 but chemical. The spectral light tiap is used in the way a'f<=*<'y 

 described ; the organisms to be observed are not coloured, Imt 

 bacteria of that common sort which twenty years ago we used 

 to call Bacterium termo, and which is recognised as the ordinal 

 determining cause of putrefaction. These organisms do not care 

 for life, but are great oxygen-lovers. Consequently, if y" 

 illuminate with your spectrum a filament of a confervoid alg«, 

 placed in water containing bacteria, the assimilation of carbon 

 and consequent disengagement of oxygen is most active in the 

 part of the filament which receives the red rays (B to C). l" 



1 Eneelmann, " Bacterium photometricum," 0»*r2«/l. ^*^"? j f''!,; 

 Utrecht, vol. vii. p. lao ; also Ueber Lichl-u. Farbeliperception nieaersici 

 Organismen, P/tiigcr's Arch, vi>I. .\>ix. p. 3^7. 



NO. I 2a6. vol.. 48] 



