680 BOOK NOTICES

BOOK NOTICES Methods of Studying the Functions of

the Different Organs of the Body. Organs of Sense: Light Sense and the Eye. I. Examination of the Eye in Red Free Light, by A- Vogt of Basel. II. Retinal Functions, by Adolf Basler of Tubingen. III. Meth­ods of Representing Nystagmus, by H. J. L. Struycken, of Breda. In the "Handbuch der biologischen Ar-beitsmethoden,'' edited by Geh. Med. -Rat. Prof. Dr. Emil Abderhalden, Director of the Physiologic Institute of the University of Halle, a. d. Saale. Abt. V, Teil 6, Ht. 3, p. 365-462. Published by Urban and Sch-warzenberg, Berlin and Vienna. This book consists of 98 pages, with

70 illustrations, one of which is a col­ored drawing of retinal atrophy as seen with the red free light. The paper is of good quality and the printing is good. References are found either in the text or as foot notes, either of which, and especially the combination, is inferior to having them .at the end of the article.

I. This part covers 14 pages, and is subdivided into three parts: (1) de­scription of the apparatus employed, (2) technic of its use, and (3) the ap­pearance of the fundus in red free light. Under ordinary illumination, there arc two components of the light reflected from the fundus: one, the "retinal light," which is only slightly altered, and the other, the "choroidal light," which is colored red by the blood thru which it passes, and usually overshadows the "retinal light." By use nf the red free light, however, the. conditions are reversed, as the retina is converted into a more or less opaque medium, giving more reflection and showing up the more anterior layers of the retina better than the posterior. The macula is shown in its true yellow color, and its changes are made more manifest. Finer ana more numerous blood vessels, hemorrhages, etc. are shown in the rest of the fundus, as well as the normal state and the pathologic appearances of the nerve fibers.

II. This part covers 76 pages, and

is treated under the following head­ings:

I. Methods of examining the relation between vision and the retina.

Monocular visual field, (a) Defects and the blind spot, (b) Limits (ex­amination with the perimeter.) (c) The macula: (1) general; (2) the macro-scope; (3) entopic observations of the yellow spot. (2) The light perceiving retinal layer. (3) Mechanical irrita­tion of the retina.

II. Methods of examining visual sen­sations without reference to their re­lation to the retina.

(1) Threshold determination. (a) Brightness threshold; (1) differential threshold; (2) absolute threshold; (3) method of estimating the smallest amount of energy necessary to stimu­late the retina, (b) Time threshold. (c) Quantitative threshold.

(2) Duration of the sensation. (3) Spatial sense, (a) Visual acuity.

(b) Delicacy of the optic localising power, (c) Irradiation.

(4) Perception of movements, (a) Velocity threshold: (1) lower thres­hold; (2) upper threshold, (b) Meth­ods of examining other facts of the perception of movement, (c) Quanti­tative threshold of movements: (1) minimizing the movement thru great distance from the eye; (2) mechanical minimizing; (3) optical minimizing. (d) Quantitative threshold of move­ment at the periphery of the visual field. (e) Brightness threshold, for movements, (f) Pseudomovements: (1) movement after images; (2) simul­taneous pseudomovements.

(5) Blending of brightnesses, (a) Methods of blending, (b) Method of demonstrating Talbot's law.

(6) Blending of forms. (7) Cinematographic sensations. (8) Intermittent illumination. Many of the above are of academic

importance only, but many are of great practical importance.

III. The third part occupies 8 pages, and consists chiefly of a description of the method of photographing nystag-mic movements,

C. L.