dentally shows the dearth of equipment for this work in English colleges.-Ed.] Under the title of psycho-physiology may be comprised these investigations in psychology which have explicit or tacit reference to the concomitant physiological processes and which are characterized by the application of the experiment method. The boundaries of the subject are somewhat ill-defined, since it shades off into physiology on the one hand and into introspective psychology on the other. I shall endeavor in this article to indicate the scope of such experimental investigations. A chick, not many hours old, will peck with fair but not complete accuracy at any small object which catches its eye. Here we have a reflex and responsive action. A stimulus is received in a sense organ; an impulse is carried centripetally along ingoing or afferent nerve fibers; certain nerve centers are thrown into activity, and an outgoing impulse is carried by efferent nerve fibers to muscles which are thus thrown into coordinated activity. It is probable that on the first occurrence of such an action it is purely automatic and is performed in virtue of the possession by the chick of an inherited organic mechanism. It is accompanied by, but not guided by, consciousness. Such guidance, however, soon becomes evident. Throw to a chick two or three days old half a dozen caterpillars, some of them common "loopers," others yellow and black "cinnabars." In the absence of previous experience they will be equally seized. But the loopers will be swallowed, while the cinnabars will be dropped. Repeat the experiment next day. The loopers will be gobbled up at once. The cinnabars will remain almost, if not quite, untouched. An association has been formed between the sight and taste in the two cases. Consciousness is no longer merely an accompaniment of the action. It controls, enforcing the action in one case, inhibiting or restraining it in another. It is probable that in the higher parts of the brain there are special centers, the physiological functioning of which is associated with this conscious control. Such activities of the chick, first those which are merely responsive and automatic, secondly those which are under conscious control, exemplify a wide range of activities both in animals and man. Let us note the scope of the experimental work that they suggest. First, there is the nature and range of stimulation of the nerve endings in the sense organ. Secondly, there is the nature and rate of transmission of the impulses along the nerve fibers afferent and efferent. Thirdly, there are the nature and localization of the activities of the automatic centers, and the time occupied by their peculiar functioning. Fourthly, there is the physiological and psychological investigation of the nature and mode of origin of the consciousness which accompanies the movements of parts of the body during response. Fifthly, there are the conditions, psychological and physiological, of association. And sixthly, there is the mode of application of the control and the localization of specialized control centers, together with the estimation of the time element in control. All these have been made the subject of careful and systematic inquiry by the method of experiment. In all cases such experimental investigation has led, if not to brilliant positive results, at all events to salutary acknowledgment of ignorance. Difficulties of interpretation abound. Nowhere are these difficulties greater than in the investigation of the physiology and psychology of color vision. Take a dozen individuals and get them successively to indicate by means of the cross fibers of the spectroscope how far they can see along the spectrum, first in the direction of the extreme red, then in the direction of the extreme violet. You will find marked differences. Perhaps one will show a quite unusual amount of variation, and you will probably find by other tests that he is color-blind. Is this variation in the retina or in the visual center of the brain? It is well known that the psychophysiology of vision is still a matter under discussion. One of the dif ficulties seems to arise from the fact that what is physiologically complex is psychologically simple. Purple gives a simple psycholog ical sensation; but it is due to a combination of physiological impulses, the coalescence or synthesis of which is, so to speak, below the threshold of consciousness. One can not, or I can not, psychologically analyze purple into its constituents, as one can analyze a musical chord. There is still a wide field for research in the psychophysiology of sensation. An important line of investigation which has now been followed up for many years deals, not with differences of kind or of quality in sensation, but with variations in intensity. Given a stimulus which excites sensation; now diminish it on the one hand until it ceases to excite sensation, and increase it on the other hand until it reaches a maximum of sensation. Then formulate the law which shall express the relation which increase of stimulation bears to the increase of sensation. The results of Weber's researches went to show that we must look not to the absolute but to the relative increments of stimulus; and Fechner, extending and generalizing Weber's results, formulated the law of the relations thus: When the stimuli increase in geometrical progression, the sensations increase in arithmetical progression, or the sensation is proportional to the logarithm of its stimulus. Concerning this law and its philosophical raison d'etre there has been much animated discussion, into which I do not propose here to enter. Suffice it to say that if we represent by a curve the rise of sensation from the threshold where it first dawns to its maximum, the law seems to hold good only for the mid-region. Various methods of experimen tation are employed. Weber and Fechner employed chiefly the method of tabulating the just discernible differences in sensation-of increas ing, that is to say, the intensity of the stimulus, and noting when this increment is just perceptible. Others, using larger intervals, have employed the method of estimating equal increments. Others, again, have constantly doubled the stimulus and noted the change in sensation. In all cases it must be remembered that what we are really dealing with is the perception of the relations between certain given sensations. This is a fact too often lost sight of. We have to infer from these relations the intensity curve in sensation. Researches on the rate of transmission of impulses along the afferent and efferent nerves may be regarded as mainly physiological. Suffice it to say that the rate is about 120 feet per second for ingoing impulses, and about 110 feet per second for outgoing impulses. Transmission in the spinal cord appears to be less rapid. The results of experimental investigations on the localization of function in the brain appear to justify the hypothesis that the automatic centers or the centers concerned in merely organic response-are quite distinct from the control centers, which are probably restricted to the cerebral cortex. It is a good working hypothesis that the centers which minister to control are the seat of those molecular disturbances which are concomitant with consciousness. Consciousness apart from control would be a mere epiphenomenon of no practical use to the organism. It is scarcely necessary for me to do more than remind the reader of the conspicuous success which has crowned the efforts of those who have patiently and systematically applied the experimental method to the localization of the centers of motor control. The motor regions of the hemispheres have now been mapped out with considerable exactitude. In all this field of research, as in the transmission of impulses, we are experimenting more on the physiological than on the psychological side of psycho-physiology. When we come to association, very little that is exact and assured is known of the physiological aspect. It is said that association tractsthat is, groups of fibers connecting together the several centers in the cerebral cortex-are almost, if not quite, absent at birth, and are established during the development of experience, which may well enough be so; but what may be the physiological conditions of their development we can at present only guess. On the psychological side much has been written on association, and in recent times Mr. Francis Galton, followed by Trautscholdt and others, has carried out experiments with the object of estimating the time that clapses between the recep tion of a simple impression and the occurrence of a simple idea suggested thereby. Such time would seem to be about three-quarters of a second. Much attention has been paid to what is termed "reaction time"; that is, the time which elapses between a given simple stimulation and the resulting responsive motion. This was found by Lange to vary according as the person who is being tested directs his attention to the expected sense-impression or the anticipated motor response. In the case of a simple response to a visual stimulus, the reaction time in the former case is rather more than one-fourth of a second, but in the latter case only about oue-sixth of a second. Practice tends to shorten the time, while fatigue lengthens it. A premonitory signal just before the stimulation markedly shortens it. Other experiments have been conducted with a view to ascertaining the time taken in simple cases of discrimination. This, too, varies very much with practice, and it is questionable whether the shorter time-values measure an act of discrimination properly so called. This part of the subject is full of diffi culties in the interpretation of the results obtained. * Enough has now been said to indicate the kind of work on experimental lines which is being done in psychophysiology. In England, while valuable researches have been prosecuted in cerebral localization, comparatively little has been done on the lines which are followed up in the German and American psychological laboratories, though Mr. Francis Galton's valuable psychometric observations have been based on somewhat similar methods. * Is it too much to hope that the time is not far distant when there shall be established in England chairs of zoological and experimental psychology, the occupants of which shall have the direction of adequately equipped laboratories, wherein systematic observations, on the lines I have above indicated, may be conducted? (Nature, March 20, 1894, pp. 504, 505.) BIBLIOGRAPHY OF PSYCHOLOGY, 1893-94. ARRÉAT, LUCIEN. Mémoire et imagination. Paris, 1894. BAIN, ALEXANDER. The senses and the intellect. 4th ed. 32703. 120. New York, 1894. pp. BALDWIN, JAMES MARK. Elements of psychology. New York, 1893. 120. pp. xvi +372. Handbook of psychology. Feeling and will. 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