LITERARY NOTICES.

Nagel, W. (Herausgeber). Handbuch der Physiologie des Menchen.

Dritter

Band (Physiologie der Sinne,, Erste Hälfte, XII+ 282, 1904. Braunschweig, Vieweg und Sohn.

This first installment of NAGEL'S "Handbuch" forms a little more than a third of the volume devoted to sense-physiology, and, except for two short introductory articles on the doctrine of specific energies (NAGEL, Berlin, pp. 1-15), and the psychology of the senses (v. KRIES, Freiburg, pp. 16-29), it is confined to physiological optics. SCHENCK (Marburg) presents dioptrics and the accommodation of the eye (pp. 30-90); NAGEL, the effects of light on the retina (pp. 1-108); and v. KRIES, visual sensation (pp. 109-282). Visual perception, and the nutrition and the protective organs of the eye are left for the second half of the volume and will not, therefore, be considered in the present review.

Both introductory articles deal with certain concepts common to all the senses. To place JOHANNES MÜLLER's doctrine of specific energies beyond dispute, it would be necessary to show that different stimuli, acting on the same nerve, produce the same sensation. NAGEL mentions that the only really clear confirmation of this kind is the taste sensations that result when the chorda in the cavum tympani is mechanically, electrically or chemically stimulated He concludes that while the doctrine, with certain reservations in the case of the lower senses, is doubtless in general valid, the efforts, dating from HELMHOLTZ, to show the existence of separate nerves with correspondent specific energies within the individual sense-organs are not successful; for the differences in sensation may just as well be due to the differences in the outward stimuli as to the specific energies of the ner ve fibers themselves.

V. KRIES's introductory discussion of the psychology of the senses is important chiefly as a general estimate of the value of psychological analysis for sense-physiology, a question which receives repeatedly more specific attention in his longer article on visual sensation. Of special interest is his view of the theoretical possibility of measuring sensations (FECHNER'S Psychophysic Law), and his treatment of the theory of specific comparisons, i.e. comparisons between sensations

that are not wholly alike, "but between which, in addition to a definite difference, a certain similarity exists" (p. 22).

The first two articles on vision proper, dioptrics (SCHENCK), and the influence of light on the Retina (NAGEL), bring up to date what is known about these more objective phenomena of physiological optics. A colored plate, in the latter, shows well the movements of the cones and the pigment of the retina.

Nearly two thirds of the present half-volume are occupied by v. KRIES'S suggestive and subtle contribution to visual sensation. The essay is subdivided as follows: laws of color-mixture, visual sensations and their psychological ordering, dichromatic color systems, adaptation of the visual organ, eccentric vision, after-images, local and color changes in the disposition (Umstimmung) of the visual organ, temporal relations of the effects of light, induced light and color sensations, limits of perception and discrimination, modifications in the color sense brought about experimentally or by disease, effects of inadequate stimuli, review of the facts and the results considered with reference to the theoretical conception of the visual organ.

It is possible to consider here only two points, -the author's general methodological views, and his estimate of present achievements in fact and theory.

As to the first point, it is evident that at almost every step the author feels the necessity of separating sharply the psychological method, "for which the mutual relations of the sensations are of chief importance, their dependence on stimuli, however, of lesser significance" (p. 109), from the physiological method, for which the paramount problem is the relation of the reactions of the visual apparatus, as indicated by the sensations, to its adequate stimuli, and of the resulting facts to the objectively demonstrable properties of the visual organs. An instance of the latter method is, of course, the attempt to refer "day-vision" to the cones, and "twilight vision" to the rods. V. KRIES admits the possibility of a psychological analysis of the sensations, but, since he questions certain current psychological inferences drawn from such analysis, and condemns attempts to reach, through a psychological ordering of the sensations, conclusions concerning the physiological processes involved, he is skeptical as to the value of the analysis. It is possible, for instance, with AUBERT and HERING, to pick out red, yellow, green and blue as four colors having no mutual resemblances in quality, but "an unbiassed person would hardly select blue in complying with a request to designate a sensation which is the contrary of yellow" (p. 135). It is doubtful, namely, whether the

often accepted oppositional relation between red-green and yellow-blue owes its existence to aught inherent in the psychological analysis itself. Similar doubt besets other such conclusions. Considering, then, the uncertain charater of even the psychological inferences drawn from an analysis of the sensations, it is far more precarious to draw conclusions as to the physiological processes involved. The author's general attitude towards the whole question, aside from the specific case just referred to, is given in his introductory paper, already briefly mentioned, in connection with his discussion of the theory of specific comparisons. The point discussed is the validity of assuming, from the possibility of making comparisons of similarity between sensations unlike in quality (e.g. similarity in brightness of two different colors) the existence of identical psychological or physiological elements which determine such similarity. "If a physiological or a pyschological theory leads us to assume in all [light] sensations a definite element, which determines our impressions of brightness, then we may, on the basis of the theory, correctly refer to the equality or inequality of that element; but we may not, conversely, deduce from the possibility of a brightnesscomparison the existence of such an element" (p. 28). The insistence is, it is clear, so far as physiological inference is concerned, on the use of only those physiological concepts in explanation which result logically from a physiological theory based on recognized physiological procedure (e.g. the response of a sense organ to its adequate stimuli), and not on detached psychological analysis.

The second point that I wished to bring forward,-v. KRIES'S estimate of the achievements of research in visual sensation, may be best stated in his own language: "If, in closing, we summarize how far theoretical concepts make it possible for us to elucidate and interpret the facts, and indicate, in general, the state of our problem, we may perhaps say, as of chief importance, that the view which we have characterized as 'Duplizitätstheorie' explains in a wholly satisfactory way a large number of functionally related phenomena This theory regards the rods, containing visual purple, as the organs of 'twilight vision,' and the cones as mediating a relatively different mode of vision, which we have called 'day vision.' One may further consider, in the light of a zone theory [Zonentheorie], the elements that mediate day vision as composed in their peripheral segments of red, green and violet components, on the relative degrees of activity of which the character of the sensations in part depends; in part, however, on other [more central] factors, which lead us to assume special conditions of color vision [Farbigkeit], to distinguish, namely, on one hand a red-green

and on the other a yellow-blue sense. With these assumptions one may take account not, to be sure, of all, but nevertheless of a very great number of the known facts. We may, indeed, represent the protanopic [red-blind] and the deuteranopic [green-blind] visual organs as originating in a lack of the red and green components respectively, the 'rotanomale' and the 'grünanomale' in a variation in the nature of the red or the green component, and the color blindness of the eccentric regions of the retina, as well as acquired color blindness, in a lack of the more centrally conditioned red-green and yellow-blue senses; we are then in a position to represent simply the large number of facts that are found in the vision of these various individuals, or of the various parts of the visual organ, and to account for them, with simple presuppositions, in a way throughout and exactly (so far as we can say) in accord with experience."

To exhaust the significance of this passage would require a synopsis of the whole article. The essence of the "Duplizitätstheorie" (for which it is hard to find a good translation) is, however, that the retina. is a twofold visual apparatus, the rods, capable of "dark-adaptation,” mediating colorless light in the presence of weak stimuli (twilight vision), and the cones, scarcely influenced by such adaptation, mediating our ordinary color (day) vision. This is perhaps the most widely accepted assumption in visual sensation, and to V. KRIES is due the chief credit of its experimental development. The zone theory assumes the validity of the triple-component theory (YOUNG-HELMHOLTZ) for peripherally situated visual elements, the possibility, however, in order to explain certain facts referred to in the quoted passage, of a fourfold division of elements, which form the basis of AUBERT's and HERING'S thought, for the central [brain] portions of the visual apparatus.

Since the article is in no sense a defence or a criticism of any exclusive theory, but rather a calm attempt to do justice, in both fact and theory, to the various and perplexing results of accomplished research, it would be inept, in this short review, to attempt to epitomize the arguments for or against the various theories. One feels, however, that the effect of v. KRIES's present contribution will be to win still more serious consideration for HELMHOLTZ'S general point of view, and to raise further questionings as to whether HERING's theory can so legitimately account for the manifold facts as is often assumed. One awaits therefore, with considerable interest, the appearance of HERINGS' pronounced volume for "GRAEFE-SAEMISCH'S Handbuch."

It is a pleasure to read v. KRIES; for, while the style is often involved (at least for a foreigner) and occasionally abstract, the exposition

is so objective, the discussion so subtle and free from polemic, the whole spirit so just, that one may well devote time and effort to master this latest and fullest review of visual sensation.

R. P. ANGIER #

Meehan, Joseph. The Berlin "Thinking" Horse. Nature. 1904, 70, 602, 603.

Cole, R. Langton. Thinking Cats. Nature, 1904 71, 31.

Both of these articles were called forth by notes which had appeared in previous numbers of Nature. The first is in response to a note in Vol. 70, p. 510 (Sept. 22, 1904), stating that a committee which had examined the performances of a horse at Berlin, known as "Clever Hans," had decided that several remarkable things he was capable of doing were not "tricks," but "due to the mental powers of the animal." Mr. MEEHAN takes exception to this view on the ground that fully as wonderful performances of a horse named "Mahomet" he knows to have been tricks pure and simple, the horse being entirely dependent upon the prompting of his trainer. He cites also a similar case of a collie dog which could spell out words by selecting the proper letters of the alphabet, play a game of cards, etc., and explains that the trick was accomplished by slight and almost unnoticeable signals given by its trainer. Mr. MEEHAN mentions a cat which climbs a doorpost and opens the latch with her paw, and this he thinks "for a cat is more wonderful than are all the performances of the Berlin 'thinking horse' for a steed." It is apparently this observation which called out a note by "Y. N." in Nature Vol. 71, p. 9 (Nov. 3, 1904) and that referred to by the second title given above, both of which relate anecdotes which are supposed to bear on the "thinking" powers of

cats.

LEON J. COLE

van Rynberk, G. Tentativi di localizzazioni funzionali nel cervelletto. Archivio di Fisiologia, Vol. I, pp. 569-574, 1904.

The investigator follows the anatomical scheme of BOLK (Grundlinien der vergleichenden Anatomie der Säugetiere, Monatschrift für Psychiatrie und Neurologie, Bd. XII, S. 432, 1902) and finds that a partial lesion of the lobulus simplex of the cerebellum in the dog causes unstable oscillations of the head. From this he concludes that the lobulus simplex is the control center for the muscles of the neck.

J. C. B.

Baglioni, Silvestro. Contributo alla fisiologia sperimentale dei movimenti riflessi; specificità qualitativa degli stimoli e specificità qualitativa dei riflessi. Archivio di Fisiologia, Vol. I, pp. 575-585, 1904.

An interesting study of certain respiratory and other reflexes in