PHYSIOLOGICAL AND METRIC SPACE 13
in the sensation, which qualitatively is the same, some differentiating constituent which is due to the specific character of the elementary organ or spot irritated, or, as Hering would say, to the locality of the attention. Conditions resembling those which hold for the skin doubtless also obtain for the extended surface of any sensory organ; although, as in the case of the retina, the facts are here somewhat more complicated. Instead of movements for protection or flight, may appear also, conformably with the quality of the irritation, movements1 of attack, the form of which is also determined by the spot irritated. The snapping reflex of the frog, which is produced optically, and the picking of young chicks, may serve as examples. The perfect biological adaptation of large groups of connected elementary organs among one another is thus very distinctly expressed in the perception of space.
ALL SENSATION SPATIAL IN CHARACTER,
This natural and ingenuous view leads directly to the theory advanced by Prof. William James, according to which every sensation is in part spatial in character; a distinct locality, determined by the element irritated, being its invariable accompaniment. Since generally a plurality of elements enters into play, voluminousness would also have to
*I accept, it will be seen, in a somewhat modified and extended form, the opinion advanced by Wlassak. Cf. his beautiful remarks, "Ueber die statischen Ftmetionen des Ohrlaby-rinths," Vierteljdhrssch. f. w. Philos, XVII. 1 s. 29.