Popular Science Monthly/Volume 72/June 1908/The Movement Towards Physiological Psychology I

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THE

POPULAR SCIENCE

MONTHLY

 

JUNE, 1908




THE MOVEMENT TOWARDS "PHYSIOLOGICAL" PSYCHOLOGY. I
By Professor R. M. WENLEY

UNIVERSITY OF MICHIGAN

LIKE many words of broad sweep and intensive significance, the term "soul" has descended to us laden with centuries of righteousness—and iniquity. Even yet some folk roll it as a sweet morsel under the tongue; while others, seeing it is neither hot nor cold, would spew it from their mouths forthwith. Consequently, whereas the very title "psychology" means a study of the soul, to-day one seldom hears the too suggestive name inside a psychological laboratory, for there we have no inclination to the double entendre. And the impression has gone abroad that this altered attitude dates from very recent times. Accordingly, it is necessary to point out, first, that traces of a psychology rooted in physiology, that is, of psychology as a natural science, did not begin yesterday, indeed, they may be said to antedate physiology itself. Thus, while it may be needless to consider Pythagoras's alleged discovery, that the tones in an octave are results of relations between physiological movements capable of numerical measurement, or Aristotle's extraordinary prevision, of the study of xxx as a matter for the physiologist,[1] we can not omit reference to post-Renascence thought.

As happens so often, especially when a recent movement attains its heyday, the "heroes before Agamemnon" are apt to be robbed of all credit. Flushed by the success of experimental methods, some have tended to forget that the forerunners did but what they could. To accuse them of interrogating themselves "without information, experience, apparatus, or means of procedure,"[2] to blame them for their inexactness and mysticism, or for their subservience to preconceived beliefs, to individual fancies and predilections, is to evince lack of historical sense. They groped in the dim, grey dawn of science, without our advantages, but they set the problems which we attack hopefully in the bright glow of early morning. If, then, we remember this, we shall be less surprised to learn that, leaving many lesser lights aside, at least two dozen men, between Locke (1690) and Lewes (1860), play their preparatory parts to Fechner, Wundt and the devoted contemporary group of psychological coworkers. To make this clearer, let me adduce some names, adding the approximate dates of most significant activity. Locke, 1690; Berkeley, 1709; Lavatar, 1772; Kant, 1781; Herder, 1785; Galvani, 1786; Cabanis, 1801; Volta, 1801; Gall, 1805; Spurzheim, 1813; Young, 1807; Sir Charles Bell, 1811; George Combe, 1820; Herbart, 1825; Fourier, 1825; Js. Müller, 1835; Beneke, 1835; E. H. Weber, 1846; du Bois Reymond, 1818; Lotze, 1852; Helmholtz. 1856; Bain, 1857; Lewes, 1860; Fechner, 1860; Wundt (1874), the inheritor of all this renown, who, in a manner parallels for psychology Darwin's position in natural history.

Our next task is to unravel the tangled skein of investigation and tentative hypotheses, of discovery and unsolved problems, for which these names stand. This is no easy thing, because some of the threads can not be disentangled. But we may contrive to render the situation less puzzling, and so see how we came to stand where we have been for the past twenty years.

Premising that they cross, recross, and even coincide occasionally, three lines of development may be traced. These are: First, the philosophical, in the accepted sense of this term, which originates, of course, in a view of human experience as a whole, or, restricting the compass somewhat, emphasizes the gross organization of consciousness; second, the physical, which lays stress on the relation of certain events in consciousness to objects presented under the primary conditions of space and time; third, the physiological, which founds on the interconnection between conscious processes and the structures of the body, particularly the cerebro-spinal system. As every one knows, the first appeared earliest, while the second and third, being dependent upon the advance of positive science, had to await what we may call the Newtonian and genetic epochs, the one initiated by Copernicus, the other by Herder and Schelling. Till the age of Kant, philosophy and physics are dominated by British thought, all things considered: from Kant till the first quarter of the nineteenth century French thought acquired increased importance; thereafter, the primacy passed to Germany, where it still remains, the influence of Darwinian ideas aside (and so I shall omit reference to the later British school). For, physiology and physiological psychology, along with the problems issuing from the new outlook, are German products in the main. The synthesis of information constituting the modern science of consciousness was "made in Germany."

 
I

The point of departure, then, lies in the philosophical line. Little as he could foresee the future influence of his theory, Locke raised, in a manner, the entire question of the relation between consciousness and the physiological organism by his famous distinction between the primary and secondary qualities of body.[3] Qualities like color, odor, hardness and sound, he called secondary, because they can not become effective components of consciousness unless the appropriate organs cooperate. Neither color nor sound resides in nature, but motions of such and such amplitude. For us, therefore, color and sound happen to be interpretations by eye and ear of something incommensurable with the perceptions in consciousness. On the contrary, qualities such as resistance and extension belong to objects in their own right, and persist independent of any cooperation by our sense organs. Locke did not grasp the philosophical problems, involved here, much less the extreme complexity of the physiological processes he assumed. However, he does advert to one of the difficulties embedded in his view—the "mystery," as it remains even yet, of space perception:

I shall here insert a problem of that very ingenious and studious promoter of real knowledge, the learned and worthy Mr. Molineux, which he was pleased to send me in a letter some months since; and it is this:—"Suppose a man born blind, and now adult, and taught by his touch to distinguish between a cube and a sphere of the same metal, and nighly of the same bigness, so as to tell, when he felt one and the other, which is the cube, which the sphere. Suppose then the cube and the sphere placed on a table, and the blind man be made to see:quaere, whether by his sight, before he touched them, he could now distinguish and tell which is the globe, which the cube?" To which the acute and judicious proposer answers, "Not. For, though he has obtained the experience of how a globe, how a cube affects his touch, yet he has not yet obtained the experience that what affects his touch so or so, must affect his sight so or so; or that a protuberant angle in the cube, that pressed his hand unequally, shall appear to his eye as it does in the cube."—I agree with this thinking gentleman, whom I am proud to call my friend, in his answer to this problem; and am of opinion that the blind man, at first sight, would not be able with certainty to say which was the globe, which the cube, whilst he only saw them; though he could unerringly name them by his touch, and certainly distinguish them by the difference of their figures felt. This I have set down, and leave with my reader, as an occasion for him to consider how much he may be beholden to experience, improvement and acquired notions, where he thinks he had not the least use of, or help from them.[4]

As the last sentence indicates, this reference remains incidental rather than determining for Locke.

It was left for his successor and critic Berkeley to give special form to the problem for its own sake, in his "Essay towards a New Theory of Vision" (1709). With remarkable prescience, he writes:

Rightly to conceive the business in hand, we must carefully distinguish between the ideas of sight and touch, between the visible and tangible eye; for certainly on the tangible eye nothing either is or seems to be painted. Again, the visible eye, as well as all other visible objects, hath been shown to exist only in the mind; which, perceiving its own ideas, and comparing them together, does call some pictures in respect to others. What hath been said, being rightly comprehended and laid together, does, I think, afford a full and genuine explanation of the erect appearance of objects—which phenomenon, I must confess, I do not see how it can be explained by any theories of vision hitherto made public. In treating of these things, the use of language is apt to occasion some obscurity and confusion, and create in us wrong ideas. For, language, being accommodated to the common notions and prejudices of men, it is scarce possible to deliver the naked and precise truth, without great circumlocution, impropriety, and (to an unwary reader) seeming contradictions.[5]

That is to say, Berkeley insists upon the necessity for another and more concrete analysis than that afforded by the resources of descriptive language.

Later, in "The Principles of Human Knowledge," Part I., he seems to indicate that this profounder analysis must take a physiological direction:

The philosophic consideration of motion doth not imply the being of an absolute Space, distinct from that which is perceived by sense, and related to bodies.... When I excite a motion in some part of my body, if it be free or without resistance, I say there is Space. But if I find a resistance, then I say there is Body: and in proportion as the resistance to motion is lesser or greater, I say the space is more or less pure.... When, therefore, supposing all the world to be annihilated besides my own body, I say there still remains pure Space; thereby nothing else is meant but only that I conceive it possible for the limbs of my body to be moved on all sides without the least resistance: but if that too were annihilated then there could be no motion, and consequently no Space.[6]

Knowing little of physiology, Berkeley leaves the problem, stated so far, indeed, but only stated. It is this: How can we derive space, a general condition of external objects, from states of the body which, in their very nature, differ utterly from this, their product? Twenty-two years later, he returns to the question, and appears to raise it in fresh form. In the Fourth Dialogue of "Alciphron, the Minute Philosopher," he says:

(Euphranor speaks:) "We perceive distance, not immediately, but by mediation of a sign, which hath no likeness to it, or necessary connection with it, but only suggests it from repeated experience, as words do things." (Alciphron replies:) "Hold, Euphranor: now I think of it, the writers in optics tell us of an angle made by the two optic axes, where they meet in the visible point or object; which angle, the obtuser it is the nearer it shows the object to be, and by how much the acuter, by so much the farther off; and this from a necessary demonstrable connection."[7]

It is needless to add that Berkeley, although he makes physiological reference and research inevitable, lived long before such a study of "local signs" as that undertaken by Lotze was practicable.

Thus, the "mystery" is simply held over, to be attacked by Kant, in whose person eighteenth century thought was to give place to a very contrasted movement. For him, space and time, the general forms of human perception of all events in consciousness, are factors not derived from materials supplied by sensation. They belong to the unifying power of perception in its relation to objects which, again, demands the presence of elements presented by sensation. Accordingly, he is quite clear that, for example, geometrical truth must be classed as a priori; that is, it can not be distilled, as it were, from those sense materials acquired in the course of experience. Thus Kant forces us to class him as a "nativist." So it does not surprise us to observe that he fails to envisage difficulties which were to become capital for physiological psychology at a later time. For instance: How, as a matter of fact, do we construct our completed perception of space? Granted that it be the product of psychical processes, what are they? Granted that it become effective only in the presence of objects, which presuppose sensuous matter, What does this physiological reference gift to our perception? Or, once more, by what subtle alchemy can we explain the obvious fact that we distribute our sensations in space, as it were? How, that is, can we account for localization? Here we quit the philosophical line for a while, observing that its unanswered questions will reappear in an altered perspective.

 
II

In the realm of physics, prior to the systematic inquiries of the nineteenth century, several more or less sporadic references to the connection between physical and psychical phenomena occur. Such, for example, were the discussions, by Euler and Daniel Bernouilli, of "the law governing the motions of strings";[8] Bernouilli's theory of the mensura sortis,[9] with Laplace's addition of the fortune physique and the fortune morale. These forecast the laws of psycho-physical relationship formulated by E. H. Weber and Fechner. Similarly, the discoveries of Galvani and Volta led to speculations on a supposed parallelism between the known phenomena of electricity and the so-called "discharges" of innervation which, in a way, plumbed the depths of quasi-charlatanism in the developments from Mesmer, and touched the heights of scientific advance in du Bois Reymond's classical work "Untersuchungen über thierische Electricität" (1848), where the mystical and the physical views passed over into physiology for systematic clarification.

Again, Fourier's Law, that "any given regular periodic form of vibration can always be produced by the addition of simple vibrations, having vibrational numbers which are once, twice, thrice, four times, etc., as great as the vibrational number of the given motion";[10] Ohm's analysis of the "periodic motions perceived by the human ear,"[11] and Wheatstone's stereoscope united to demonstrate that the psychical and the physical stand in close connection.

Finally, Young's color-theory, with its three primary colors—red, green and violet—paved the way for a passage from physical to physiological considerations; for it led to the hypothesis of "specific energies" in the nerve-fibers.

Ere we pass to the epoch-making transformations of last century, two movements, discredited in many ways it is true, yet of importance as preparatory, demand recognition. It may surprise us to find that they are phrenology and physiognomy. Gall and Spurzheim, both physicians, substituted for the descriptive and introspective faculty-psychology an anatomical scheme parallel essentially in result. They concluded that the faculties can be localized in definite portions of the brain, and that these, in turn, can be traced by reference to the surface formation of the skull. Phrenology created wide-spread interest early in the nineteenth century—witness George Combe (1828) in Edinburgh, who, it may be interesting to relate, received a call to the chair of philosophy in the University of Michigan, or Caldwell and Godman in this country. Through a long series of fluctuating fortunes their suggestions became effective finally as elements in a scientific physiological psychology when Broca (1861) located the brain-center of speech; and, ever since, thanks to the labors of Hughlings Jackson, Ferrier, Golz, Hitzig and many others, this has provided an important sphere of study to physiological psychology.

In similar fashion, the observations, opinions and speculations of Lavatar, in his "Physiognomische Fragmente" (1772), produced a furore; elicited Sir Charles Bell's famous "Essay on the Anatomy of Expression" (1806), with its theory of the relation between intellectual power and the facial angle; and, at last, attained complete scientific consecration in Darwin's masterly book, "Expressions of the Emotions in Man and Animals" (1872).[12] Thus positive error and misleading half-truth sometimes serve to state problems which, otherwise, might have failed to gain hearing. One may conclude fairly, then, that questions about the relation of body to mind were in the air throughout the entire course of the eighteenth century and, at its close, had begun to become clamant.

 
III

At this juncture philosophical activity assumed unprecedented proportions and left a solid deposit destined to a constructive influence which, I fear, too few scientific men realize to-day. The years 1780-1840 witnessed an efflorescence of speculative thought unparalleled in western history save once—in that wonderful century (422-322 b. c.) when Socrates, Plato and Aristotle secured for the Greeks a far more permanent and formative hold over mankind than was ever achieved by Aristotle's amazing pupil, Alexander the Great. As at Athens, so in the modern period, transitive intellectual personages are legion. Here it must suffice to mention Herder, Fichte, Schelling, Hegel, Herbart and Beneke. Fichte's previsions of a social science, Schelling's wide-spread sway over nascent physiology and medicine, and Hegel's splendid mission, as founder of contemporary critico-historical and comparative studies that have altered the face of human nature, must be suppressed now. But, for psychology, Herder, Herbart and Beneke present matter of high import.

Herder possessed that rarest of endowments, a seminal mind. His thought scattered seeds everywhere, which have come to fruitage since in philology, comparative religion, anthropology and psychology, to name no others. Genetic conceptions inspired him, and his command of enormous reading enabled him to illustrate them concretely, if sporadically. Under the influence of Albrecht von Haller, the eminent Göttingen naturalist, who founded experimental and brain physiology,[13] he foresaw the necessity of physiological research for psychology. "According to my thinking," he wrote, as early as 1778, "there is no psychology possible which is not at every step definite physiology. Haller's physiological work once raised to psychology, and, like Pygmalion's statue, enlivened with mind, we shall be able to say something of thought and sensation."[14] No less remarkable is the following, in its prophetic insight; "Among millions of creatures whatever could preserve itself abides, and still after the lapse of thousands of years remains in the great harmonious order. Wild animals and tame, carnivorous and graminivorous insects, birds, fishes and man are adapted to each other."[15]

But, admitting Herder's vision to the full, his main title to a distinct place in the historical line of psychologists supplies the reason why, strange as it may seem, we must dismiss him briefly in the present context. The most recondite and, at the same time, most potent onality of self-consciousness roots in its eerie power of objectification. Students brood upon this increasingly, sciences like historical criticism, sociology and æsthetics offering testimony. Men bandy words about the "social mind," about "mob psychology," about a "national or epochal ethos," and so forth. Customs and institutions, myth and religion yield paleontological records, not of individual men, but rather of humanity, a kind of compost of individuals. But the implications hinted here receive their most striking manifestation in language. Now Herder, to give him his due, must be saluted as the herald of Völkerpsychologie and of Sprachwissenschaft. So he stands aside from the line under examination. For, even if it he recalled that phonology can be classed as a physiological science, the matter terminates there. Great as have been the contributions of W. von Humboldt, Bopp, Grimm, Max Müller and their coworkers, and much as has been accomplished by Waitz, Lazarus, Steinthal, McLennan, Spencer, Lubbock, Tylor, Frazer and Westermarck, all sit more or less loose to physiological psychology, which continues an investigation of individual far more than of group processes. So, attractive and suggestive as Herder is, perforce we rest content now with the bare reference to what I have had the temerity to call his seminal mind.

When we arrive at Herbart and Beneke the case presents a different aspect. For they stand forth among the last great psychologists who deal with mind as mind, to the exclusion of modern experimental methods applicable chiefly to the body. After a manner their services pale in the glow of the contemporary atmosphere; their work has been bemused by pedagogists, misprized overmuch by psychologists, even if, as Wundt says,[16] he owes most to Kant and Herbart, and even remembering the work of Herbartians like Drobisch, Volkmann, Exner, Strümpell, Cornelius and R. Zimmermann.[17]

Note, at the outset, that Herbart (1776-1841) and Beneke (1798-1854) revolt strongly against the dominant Hegelian school, and that both attempt a concrete study of consciousness. On one point they differ decisively. Herbart's psychology, as the title of his chief work runs—"Psychology as a Science, founded, for the first time, upon Experience, Metaphysics and Mathematics," possesses a triple basis. Beneke excludes the second and third, emphasizing experience as the sole legitimate foundation. In this respect he takes the pioneer place among those who raised the later cry, "Back to Kant!"

Thanks to the limits of this paper, Herbart's metaphysical doctrine must disappear with a word. He held that the soul, in its own proper nature, forms an original, changeless and simple entity. Psychological processes originate in its resistance to intrusion from the outside, therefore, the complexities of consciousness, just because they are complex, fall within the reach of analysis. As results of mechanical interaction they lie open to mathematical methods. Such procedure, of course, leads straight to experience, and, on the whole, it may be affirmed that, as his psychology prospers, the direct influence of his metaphysic wanes. In this way a long step towards psychology viewed as a natural science becomes easy. Let us try to see how Herbart presaged such tendencies.

He denies that consciousness consists in a bunch of faculties. Mind persists as a system of concrete relations between its constituent parts. These parts interact mutually, and therefore stand in mechanical relations to one another. As thus related, they constitute a unity of "presentation" which resists "arrest of any of its components." Accordingly, "presentations" may form series; these series, in turn, may arrest or strengthen, and shorten or intertwine, mutually. While the simple substance of soul (metaphysical) remains unknown qualitatively, its activities, in its processes of self-maintenance, afford the states of consciousness which psychology studies. In this respect the soul happens to be identical with all other "reals" which, in sum, make Herbart's universe. Therefore, methods peculiar to the positive sciences find application, and mathematical analysis becomes a chief instrument of discovery. Further, the opposition between "presentations" transforms states of consciousness into forces, with the result that a statics and dynamics (mechanics) of mind emerge. It is feasible, accordingly, to calculate the equilibrium and movement of "presentations." So, conformably to science, Herbart frames hypotheses and tries to establish them by mathematical methods. He sets himself to show accurately how the indeterminate manifold of sensation, as envisaged by Kant, and the multiplicity of ideas as set forth by the faculty-psychology, come to an organic unity in appercipient self-consciousness. In a word, the proper study of psychology is mind which, in turn, consists precisely in those transforming processes known collectively as "apperception." A very apposite delimitation of the psychological field, one would add. And it is both interesting and important to note that, in this theory of apperception, above all else, Herbart continues to speak in contemporary psychological thought. His connection with the modern movement, though by no means clear on the whole, appears in special tendencies. First, in his complete acceptance of the method of regressive analysis; second, in his appeal to experience; third, in the attention which he has compelled to the possibility of mathematical applications in this unstable sphere; fourth, in his gradual drift away from his own metaphysical basis as he wrought to render psychology a natural science—to prove that, in mind, as everywhere, natural law reigns supreme.

Notwithstanding all this, his opposition to anything in the nature of a physiological psychology seems certain. For this curious hesitation reasons must be sought, not in any antagonism peculiar to Herbart himself, as some recent experimental enthusiasts, blind to history, have fondly supposed, but in the general perspective of his age. Like many of his followers, he was a partisan enemy of the speculative philosophy that ruled Germany, and he paid the inevitable price. His judgment on certain scientific developments became warped. He perceived that Schelling's "Naturphilosophie" exercised profound influence upon much of biological science as it then stood. Physiology looked like an ally of idealism, therefore he would exclude it rigidly from psychology, as a sure source of trans-experiential contamination. On this he spoke with no uncertain sound—physiology, as he saw it, was no fit friend for a mathematico-empirical psychology. "Physiology, as an empirical doctrine, has attained a height which nobody can despise. Moreover it proceeds in the light of modern physics. Nevertheless, it has eagerly sucked up, as the sponge sucks up water, that philosophy of nature which knows nothing, because it began by construing the universe a priori. Towards this error no science has proved so weak, so little capable of resistance, as physiology."[18] The very end for which Herbart toiled so strenuously is obscured from him by his suspicion of physiological tendencies. Truly the time-spirit plays us humans queer tricks!

Free from these negative considerations, Beneke brought psychology another stage nearer science. He excluded Herbart's metaphysic, demanded concrete treatment of consciousness as the one road to real knowledge, and placed all the other philosophical disciplines in a position of dependence upon psychology. His pivotal doctrine exhibits clearly the possibility of scientific procedure in psychology. It may be put as follows. Experience presents two sides—an "outer" and an "inner." The former consists of sensational phenomena, or, as Hume would have said, "sensations, passions and emotions as they make their first appearance in the soul." The latter includes everything that relates to memory, imagination, thought and ratiocination. Thus science, which deals with the "outer." reaches indirect knowledge of being, while psychology, thanks to its immediate contact with its object ("inner"), arrives at knowledge of true reality. Consequently, by analogy from our own selfhood, we can acquire relatively sufficient knowledge of other men, this sufficiency dwindling, so to speak, as we descend in the scale of existence. Accordingly, positive science is confined to observation, but psychology considers knowledge—an inference from this same observation. Therefore the methods of science apply as much in the one sphere as in the other. In short, consciousness originates the dualism between soul and body, mind and objects. Corporeal processes become conscious in us, and thus fall under direct perception:

There is no kind of corporeal process which can not under certain circumstances become conscious, and as a conscious thing be perceived by us directly.... Such a revolutionary change of a thing usually not a psychical apprehension to a psychical apprehension, would be unthinkable were it the case that their being was in fundamental opposition: we are thus led all the more to the conclusion that both kinds of powers in their innermost nature stand very close to one another, and that for the explanation of their inner coherence and interaction no artificial hypotheses are requisite. [19]

Evidently, then, psychology investigates all that we apprehend through internal perception. If we apprehend anything by external perception, it must submit to transmutation by the "inner," in order to enter into experience as an effective component. I am unable to see that any other meaning can be read into this view than that formulated in the current theory of psycho-physical parallelism. Causal connection between body and mind there is none; and the contrasts in our inner experience of them reside in apprehension, never in actual reality. The plain business of psychology, therefore, consists in applying observation, experiment and hypothesis to the "inner." Just as with science, regressive analysis supplies the methods.

Beneke concludes that psychological processes present themselves as complexes fashioned from four primary factors. These are: (1) The transmutation of sense "excitations"; (2) the formation of new "powers"—analogous, it may be said, to the growth of new tissue; (3) the redistribution of "excitations" (sensuous) and of these new "powers" or products themselves; (4) the interpenetratation of homogeneous products, according to their degree of homogeneity. Obviously enough, redistribution, or transference, within the psychological complex forms the dominant feature; and its forcible similarity to modern energistic conceptions or, as Professor Titchener remarks acutely, "to the process by which one body becomes cooler by communicating heat to another,"[20] needs no comment. Whatever one may think of Beneke's special doctrines, he stands to his material in the attitude of a positive scientific investigator. If Herbart worked like a mathematical physicist, Beneke works like a biologist. Indeed, he reminds one of the French school of so-called "organicists"—Bichat, Claude Bernard, Delage and, perhaps, Roux. I think a specious case could be framed for a parallelism between Beneke's teaching and Claude Bernard's biological conclusion, especially as formulated in the second Leçon in the first volume of his "Leçons sur les Phénomènes de la Vie" (1874), which contains the striking declaration: "la fixité du milieu intérieur est la condition de la vie libre indépendante."[21] Be this as it may, Beneke brought psychology within the purview of scientific inquiry. Like Herbart's, his conclusions might be stigmatized, but that both made preparatory contributions there can be no reasonable doubt. The attitude they adopted is of the essence of the matter. And one ought to add that the presence of unconscious or subconscious factors in the physical process, a highly significant phenomenon, follows from the situation as contemplated by them.

  1. De Anima, I., i., 403a 25.
  2. "German Psychology of To-day," Th. Ribot, p. 5 (Eng. trans.).
  3. "Essay concerning Human Understanding," Bk. II.; Chap. VIII.
  4. "Essay concerning Human Understanding," Bk. II., Chap. IX., Sect. 8.
  5. Sects. 119-20.
  6. Sect. 116.
  7. Sect. 8.
  8. "The Sensations of Tone." Helmholtz, p. 23 (Eng. trans.).
  9. "German Psychology of To-day." Ribot, p. 226 (Eng. trans.).
  10. Helmholtz, loc. cit., p. 52.
  11. Cf. ibid., pp. 23, 51, 89, 102-3.
  12. Cf. "Physiol. Psych.," Wundt, Vol. II., pp. 598 f. (4th ed.).
  13. Cf. "The History of Physiology," Foster, pp. 291 ff.
  14. Cf. "Vom Erkennen und Empfinden der menschlichen Seele," Werke, IX.
  15. Quoted by Sully in the Encyc. Brit. (9th ed.), Vol. XI., s. v. Herder.
  16. "Physiol. Psychologie," preface to the first edition, 1874.
  17. Cf. Mind, Vol. XIV., pp. 353 ff. (old series).
  18. "Werke," VI.. p. 65.
  19. "Lehrbuch d. Psychologie als Naturwissenschaft" (1845), Sect. 48.
  20. Mind, Vol. XIV., pp. 21-2 (old series).
  21. P. 113.