June 13, 1890.] 



SCIENCE. 



357 



find, too, that all of the types of motor hallucination are ex- 

 plicable as central irritations of these centres, in which these 

 different factors are present in various degrees. The nature of 

 these centres would in each case be both sensory and motor ; and 

 the hallucination, if properly analyzed, would also be of the 

 mixed form. 



Color-Vision and Color-Blindness. 



Mr. R. Brudenell Carter,' in a lecture before the Royal Institu- 

 tion, outlined the position of modern science upon this important 

 topic, and from his remarks the following points may be selected : 

 the perceptive layer of the human retina consists of rods and 

 cones; in the centre of the retina, only cones occur; in a ring around 

 this, each cone is surrounded by a circle of rods; and as we recede 

 from the centre, the proportion of rods to cones becomes larger 

 and larger. There is good reason for believing that color-vision 

 is limited to the coues, and certainly the perception of color is 

 best where the cones are most numerous. Nocturnal animals 

 have a less perfect development of cones than diurnal ones. The 

 limitations of the color-sense on the human retina are very con- 

 siderable. The color-sense is complete for three fundamental 

 colors of the spectrum for not more than thirty degrees of the 

 field, is limited to red and violet in a small ring outside this field, 

 and from there on is sensitive only to differences of light and 

 shade. In the lower animals, especially in those having their 

 eyes more on the side of their heads and possessing acute vision, 

 we find a power of perceiving colors over a much larger area of 

 the retina ; and this is associated, as has been shown in birds, in 

 some reptiles, and in fishes, with a more abundant and more even 

 distribution of the cones over the retina. There has recently 

 been observed upon the cones of some birds, globules of a colored 

 oil, which transmit only light of their own color; and green, 

 orange, and red drops prevailed in the birds examined. Why this 

 is so remains to be determined. 



When the condition that exists normally in the outer zones of 

 the retina exists also in the centre, we have color-blindness; but 

 such a degree of color-blindness is rare, if indeed it exists at all. 

 The more common defect is that which exists in the zone sur- 

 rounding the fovea; that is, a blindness to green. Such persons 

 can distinguish violet and yellow, and they can see red, but 

 cannot distinguish it as a color from green. The most common 

 defect, however, is a blindness to red ; and an extremely rare 

 form is blindness to violet. The Young-Helmholtz theory re- 

 gards the defect in the red-blind person as a paralysis or an ab- 

 sence of the red-perceiving elements in the retina. To such a 

 one, spectral red is not absolutely invisible, but appears as a green 

 of feeble luminosity, and the brightest part of his spectrum is in 

 the blue-green. When green stimulates the eye of the green- 

 blind, there results the white of the green-blind, which to ordinary 

 eyes is sort of rose-color. To both red and green blind, then, 

 these two colors are indistinguishable, the only difference being 

 that to the red-blind the red, and to the green-blind the green, 

 seems, in comparison with the other, of feeble luminosity. By 

 looking at colored objects through a glass of peacock-blue the 

 colors will appear somewhat as they do to a red-blind person, and 

 by looking at them through a purple glass they will appear some- 

 what as they do to the green-blind. These defects exist in about 

 four per cent of the male population, and in about one-tenth of one 

 per cent of the female. 



With regard to the dangers resulting from the placing of color- 

 blind persons in responsible positions, it is easy both to exaggerate 

 and to underestimate them. We naturally think of the railway 

 and marine service, in which colored signals are used ; and it is 

 certain that a considerable number of those thus employed suffer 

 from this organic and therefore incurable defect. We would be 

 apt to think that such persons would at once reveal the defect, 

 and thus be released from duty. We must remember, however, 

 that the existence of this defect remained unknown until about a 

 hundred years ago, and that it is often concealed by the correct 

 use of color-names, — a rather easy art for the color blind to ac- 

 quire. And, again, these persons always know where to look for 

 a signal, and hence under ordinary occasions the slight distinction 

 ' See Nature, May 15, 1890. 



they makg between red and green, aided by good luck, may be 

 suflScient to avoid accidents. The methods of testing and discov- 

 ering this defect are various, but they all depend upon matching 

 colors and avoiding the use of color-names in the process. There 

 are all degrees of the defect, from a tendency to confusion of dark 

 greens and reds and a hesitation in deciding between them, to 

 absolute indistinguishability of pronounced shades of them. The 

 necessity of an examination in all posts in which color-distinction 

 is necessary is now recognized, and governmental regulations 

 upon the matter have been largely adopted. It may be advisable 

 to add that there is a form of imperfect color-perception not at all 

 related to color blindness, but sometimes confused wath it. It is 

 simply a lack of practice and of training in color distinctions. 

 It is quite surprising with what ignorance of colors and their 

 various shades children may grow up. This is a thing that may 

 be taught, and is now frequently introduced into primary educa- 

 tion. 



NOTES AND NEWS. 



Among the geographical expeditions which are decided upon 

 for next summer in Russia, one is of unusual interest, that to the 

 Black Sea. The physical features of this important and deep ba- 

 sin are so little known that we have little information on the 

 depth at even a short distance from the shore. As to the tem- 

 perature, salinity, etc., of the water at great depths, we have 

 only a few observations along the eastern coast by Professor Lap- 

 schin, and near the entrance to the Bosporus by Count Admiral 

 Makarow, Last winter, Professor Klossowsky and Dr. Andrus- 

 sow, in a memoir addressed to the council of the Imperial Russian 

 Geographical Society, showed clearly the importance of an inves- 

 tigation of the deeper part of this sea. It was warmly supported 

 by the society, and the Ministry of Marine sends a vessel for this 

 purpose on a cruise of a month's duration. The nautical part of 

 the scientific work will be under the direction of Capt. -Lieut. 

 Spindler, while the Geographical Society sends Drs. Wrangell, A. 

 Woelkof, and Andrussow, the last mentioned of whom will have 

 charge of the botany and zoology. 



— The Elizabeth Thompson Science TTund, which has been es- 

 tablished by Mrs. Elizabeth Thompson of Stamford, Conn., "for 

 the advancement and prosecution of scientific research in its 

 broadest sense," now amounts to twenty six thousand dollars. 

 As accumulated income will be available December next, the 

 trustees desire to receive applications for appropriations in aid of 

 scientific work. This endowment is not for the benefit of any one 

 department of science, but it is the intention of the trustees to 

 give the preference to those investigations which cannot other- 

 wise be provided for, which have for their object the advance- 

 ment of human knowledge or the benefit of mankind in general, 

 rather than to researches directed to the solution of questions of 

 merely local importance. Applications for assistance from this 

 fund, in order to receive consideration, must be accompanied by 

 full information, especially in regard to the following points: 1. 

 Precise amount required. Applicants are reminded that one dol- 

 lar is approximately equivalent to four English shillings, four 

 German marks, five French francs, or five Italian lire. 2. Exact 

 nature of the investigation proposed. 3. Conditions under which 

 the research is to be prosecuted. 4. Manner in which the appro- 

 priation asked for is to be expended. All applications should 

 reach before December, 1890, the secretary of the board of trus- 

 tees. Dr. C. S. Minot, Harvard Medical School, Boston, Mass., 

 U.S.A. It is intended to make new grants at the end of 1890. 

 The trustees are disinclined, for the present, to make any grant 

 exceeding three hundred dollars: decided preference will be given 

 to applications for smaller amounts. A list of the grants hitherto 

 made, amounting to about six thousand dollars, is given in a cir- 

 cular just issued by the trustees. 



— The American Swedenborg Printing and Publishing Com- 

 pany of this city are issuing the more important of Swedenborg"s 

 writings in clearly printed pocket volumes. "Angelic Wisdom 

 concerning the Divine Love and the Divine Wisdom," the latest 

 issue from their press, is a model of neatness and of good I ook 

 making. 



