Literary Notices. 171 



6. Chemical stimulation is thus shown to be electrical and dependent upon the 

 electrical charges of the ions. Electrical stimulation is produced by modifying the 

 distribution of ions in the nerve and thus altering their concentration as Nernst 

 suggested. R- M. Y. 



Baird, John Wallace. The Color Sensitivity of the Peripheral Retina. Published by the Carnegie 

 Institution of Washington, May, 1905. 80 pp. 



This paper presents a valuable historical sketch of the study of the functions of 

 the peripheral retina in addition to a statement of the results of experiments by 

 Dr. Baird. 



The object of the experiments was to determine: (i) the chromatic character 

 of the sensation aroused when a constant color stimulus is applied successively to 

 different regions of the retina; (2) the relative extension of the different retinal 

 areas within which the tones of the different color stimuli are correctly recognized. 



The results agree with those of most earlier investigations in indicating the 

 existence of three retinal zones: (l) an extreme peripheral zone on which stimuli 

 appear colorless; (2) an intermediate zone where they appear yellow or blue, and 

 (3) a central zone where they may appear red, green, yellow or blue. 



The limits of these color zones may be varied by changing the retinal adapta- 

 tion, background, magnitude of visual angle, condition of optical refraction, bright- 

 ness and saturation of the stimulus, etc. 



"Of all possible colors, there are four and only four which undergo no change 

 of tone in indirect vision. These are a purplish-red (non-spectral), a yellow 

 (about ^yofifx), bluish-green (about ^go/ifx), and a blue (about 460////)." 



The after-effects of retinal stimulation are surprisingly persistent, and in the 

 opinion of Dr. Baird they have invalidated the results of many studies in color 

 vision. 



All of the results of this investigation are interpreted by the author as in agree- 

 ment with the Hering and Franklin theories of color vision. r. m. y. 



Stern, Richard. Die Pseudomotorische Funktion der Hirnrinde. Leipzig, F. Deuticke, pp. 27. 

 1905. 



This paper is purely speculative and proposes the theory that all nervous cur- 

 rents are centripetal. Muscles lose none of their contractility by being isolated from 

 the nerves that are ordinarily supposed entirely to govern their contractions. 

 Contractility is a vital function of muscle; "and we must in all earnestness ask 

 ourselves whether it is not possible that muscle contractions normally take place 

 without any innervation coming to them from the central nervous system." Accord- 

 ing to present conceptions of sensory and motor currents, although the ganglion cells 

 are closely similar in the two kinds of nerve, "the motor cell has to generate energy, 

 while the sensory cell simply receives it. Morphologically similar structures should 

 thus seem to have diametrically opposite functions." Is it not possible that all 

 nervous currents move centripetally? 



Muscular contraction would be explained in this way: the ganglion cells of 

 motor nerves possess a spontaneous power of change; perhaps this is an ameboid 

 motion, or perhaps it is a change merely of conductivity. In this latter case, for 

 instance, if the conduction is greater in the ganglion of the motor nerve, more heat 

 is conducted away from the muscle thereto attached, and this muscle contracts. 

 If the resistance is raised, less heat is conducted and the muscle relaxes. In the 



