Sept 28, 1876] 



NATURE 



483 



phenomena. But as most admit that there are two aspects in 

 which mental phenomena may be viewed, why should not both 

 be looked at carefully ? If it be also admitted, that it is impos- 

 sible to connect any physical process (supposing we knew it) 

 occurring in brain cells with an act of consciousness, what is the 

 use of taking a one-sided view of the phenomena in question ? 

 Why not study both sides of the problem, and give up the 

 attempt at reconciliation, which is entirely beyond the pale of our 

 faculties ? This mystery of mind and matter has puzzled thought- 

 ful men from the earhest times. Some have attempted a recon- 

 ciliation. They have reasoned in a circle, so that most people, 

 after perusing their works, are no nearer an ultimate solu'.ion than 

 they were at the beginning. We always come back to this view 

 of the case, namely, that every fact of mind has two aspects, a 

 . physiological and a psychological. That is one way of looking 

 at the problem, and it is the one which, in the present state of 

 knowledge, personally I prefer. But there is another. Thus, as has 

 been well argued by Mr. George Henry Lewis in his recent work, 

 "Problems of Life and Mind," two very different descriptions 

 may be given of one and the same mental activity. The one 

 may be expressed in the language of psychology, which is the 

 language we commonly use to describe our feelings ; the other 

 may be stated in the language of physiology, a language intelli- 

 gible only to those acquainted with the present state of physio- 

 logical research. He says: "All that we have to guard 

 against, is the tendency to mistake difference of aspect for 

 difference of process, and to suppose that changes in feeling can 

 exist independently of changes in the organism, or that any 

 change in the organism can be effected otherwise than by some 

 previous change." This way of stating the question may be more 

 satisfactory to some minds. At all events, it is a fair a;.tempt to 

 solve the puzzle of our present state of existence, in which we 

 are constantly brought face to face with the antithesis of object 

 and subject. 



Abandoning these speculations which are fruitless in practical 

 effects, let me now endeavour very briefly to indicate the lines of 

 inquiry in the domain of physiology, along which progress has 

 been and may be made in the attempt to solve psychological 

 phenomena ; and I wish it to be understood that I do not take 

 these in any logical order, but merely adduce them by way of 

 illustration. It will also be my aim not so much to describe 

 what has been done in the past, as to indicate what remains to 

 be done in the future. 



Research in Physiological Psychology, 



First of all, then, it is quite evident that all researches on the 

 general physiology of the great nerve centres are of paramount 

 importance. Such researches as those of Hitzig, Fritsch, and 

 Ferrier on the excitability of the cerebral hemispheres, supplying 

 new ideas regarding the mechanism of the brain as a compound 

 organ ; of Wundt on central innervation and consciousness, in 

 which he discusses in a manner never before attempted, the phe- 

 nomena of reflex excitation ; of William Stirling on the summation 

 of excitations in reflex mechanisms ; of various French physiolo- 

 gists on the mode of action of ganglia in insectse ; and of many 

 others, are all recent important contributions to this department 

 of science. Here, however, we have to confess that we have 

 little accurate information regarding the minute structure of the 

 parts involved, and consequently no anatomical basis on which 

 to found our views. We have a general idea of strands of 

 nerve-fibres and groups of nerve-cells of various forms, but we 

 have no precise knowledge of the relative quantity of these, or of 

 the relations of one group of nerve-cells to another group. We 

 are unacquainted with any peculiarity in structure, for example, 

 by which even an accomplished histologist could identify three 

 microscopical sections as respectively portions of the brain of a 

 man, of a monkey, and of a sheep. All this has still to be 

 worked out. Every little area of brain-matter has to be surveyed 

 and carefully described. Supposing this were done in the case 

 of the human brain, and of the brains of the higher animals, the 

 same must be attempted with the brains of animals lower in the 

 scale. I can then conceive a grand collection of facts which may 

 throw light on the intricate working of different kinds of brains, 

 and, perhaps, afford a rational explanation of certain psycho- 

 logical characters. 



Suggested Investigation. 



What I mean may perhaps be better understood by a research, 

 which I would suggest by way of experiment. No one who has 

 kept an aviary of small birds — say a collection of our native 

 and foreign finches — |can have failed to observe marked 



differences of character and habits among different members of 

 the same genus, and even among different members of the 

 same species. One manifests cunning, another combative- 

 ness, a third kindness to smaller brethren, a fourth bullies 

 all about him, a fifth may usually be quiet and peaceable, but 

 occasionally gives way to uncontrollable rage, and so on. The 

 question arises, then. Have these psychological peculiarities 

 any organic basis, any explanation in the structure of the brain ? 

 or, are we to rest satisfied by asserting that these peculiarities 

 are due to the action of some kmd of psychical principle regarding 

 which we know nothing ? I have little doubt most will agree 

 that these psychical characteristics of birds depend on peculiari- 

 ties of brain structure the result of hereditary transmission through 

 many generations. If so, here we have an opportunity of exa- 

 mining the microscopical structure of small brains, relatively 

 simple, and easy of manipulation, with the view of ascertaining 

 whether or not there are any structural differences which will 

 account for these differences in psychical character. This is a 

 line of inquiry likely, in my opinion, to establish an organic basis 

 for a comparative psychology. 



After referring to recent researches on the chemistry of the 

 brain. Dr. McKendrick proceeded to refer to those on Uie physi- 

 ology of the senses, which afford another series of data for the 

 psychologist. These researches may be said to be of three 

 kinds — (i) inquiries into the anatomical and physiological me- 

 chanism of the sense organ itself, such as, in the case of vision, 

 the general structure of the eye as an optical instrument, and its 

 movements by the action of muscles, so as to secure the con- 

 ditions of monocular or binocular vision ; (2) inquiries into the 

 nature of the specific action^ of the external stimulus upon the 

 terminal organ of sense, and the transmission of the effect to the 

 brain ; as, for example, the action of light on the retina, and 

 transmission along the optic nerve ; and (3) experiments in 

 which various stimuli are permitted to act under certain con- 

 ditions on the terminal apparatus, and the result is observed and 

 recorded by the consciousness of the experimentalist himself, as 

 in researches on colour, duration of impressions on the retina, 

 positive and negative after-images, &c. By these three modes 

 of inquiry a large number of facts relating chiefly to the senses 

 of hearing and vision have been collected ; and most of these 

 facts, inasmuch as they assist him in understanding the'condi- 

 tions of sensory impressions and 'sensational effects, are of im- 

 portance to the psychologist. 



Measurement of Time in Sensory Impressions. 



The next step of importance made by physiology into the 

 domains of psychology is the measurement of time or duration 

 in sensational effects.^ This has been carefully measured by 

 objective methods. Speaking generally, the time occupied from 

 the commencement of the action of the stimulus to the termina- 

 tion of a sensation, may be divided into four portions, each 

 of which has a certain psychological interest : — First, an inter- 

 val of time is occupied by the primary physical change pro- 

 duced by the stimulus. During this interval, called the period 

 of latent stimulation, no effect is observed. Thus, when a 

 motor nerve distributed to a muscle is stimulated by a short 

 electrical shock, about i-6oth of a second passes before the 

 muscle contracts. Second, when the change in the nerve or 

 terminal organ has begun, a second interval of time is occupied 

 in the transmission of the impression to the nerve centre, which 

 is succeeded by a third interval, during which changes occur in 

 the nerve centre, and the result of which is a sensation. The 

 time occupied in transmission, or the rate of conductivity in 

 nerve, is tolerably well known, being at the rate of about 200 

 feet per second in the nerves of man ; but the time occupied in 

 the production of the sensation in the centre has not yet been 

 clearly ascertained, owing to the difficulty of supposing such a 

 sensory nerve centre to be, previous to the stimulus, in a state 

 of absolute inaction. Lastly, it has been found that when a 

 nervous action of any kind has been initiated by a stimulus, it 

 goes on for some time after the stimulus has ceased to act This 

 prolongation of the sensation may be well studied in the case of 

 impressions on the eye, where the time of the duration of the 

 impression has been measured by Helmholtz, Plateau, and others. 

 These distinguished observers also foundthat the length-Hif time 

 occupied by the after effect varied according to the intensity of 

 the light. Thus, after a weak light, the unchanged impression 

 lasts longer than with a strong light. A strong illumination is 

 followed by an after impression fading sooner than with a feeble 



' In the following observations I am much indebted to the essays of Mr. 

 James SuUyi contained in his volume, ' Sehsation and Intuition." (London.) 



