Table II gives in detail the data yielded by four of the most instructive films. C 3 is the longest record that was obtained; Tu 4 is among the shortest, though it is not the very shortest. H 2 and H 3 show how nearly alike are the simultaneous movements of the two eyes: .07 sec. is the greatest difference recorded on any film between simultaneous movements. All four records show how much less the duration of the slow movements is at the beginning of the record than at the end, and how little the fast movements vary in this respect.
H 2 is given because it is not typical; and about one half of the film itself is reproduced in Fig. 5 (Plate II). It will be seen that at four points there intervened between slow movements (toward the right) a rapid one that was also toward the right. This is the only record in which such a thing happened: and its explanation is problematical. With the subjects C and H, and only very rarely with these, a rapid movement sometimes took the place of a slow one, that is, occurred in the same direction as the slow movements (e. g., Table II, C 3). And a trifle more often, yet very seldom, a rapid movement was relatively slow (e. g., ibid.). With every subject there are a few cases in which the eyes stood still for a small part of a second (e. g., ibid.), and these moments of rest seem to come after a rapid or a slow movement indifferently.
McAllister[15] and others have shown that the eyes are seldom at rest even when voluntary fixation is attempted, and these anomalies in the nystagmiform series may well be the result of such random factors, which instead of being always inhibited by the afferent impulses from the semicircular canals, which govern the nystagmus, operate along with these latter, and sometimes even inhibit them. With the exception of these anomalies, the movements recorded in the photographs confirm the observations of Purkinje, Mach, Breuer, Delage, and other investigators.
In conclusion, the sensations of vertigo and of nausea seem not to be essentially connected with the nystagmus. Several subjects were so disagreeably affected by a preliminary rotation that it seemed best not to continue the experiment with them. With those, however, whose eyes were photographed, while they experienced a mild degree of vertigo and nausea during and after the first few rotations, these sensations soon wore off with further practice, while so far as could be observed their eye-movements were as ample and rapid as at first. The introspection of these subjects was that after the rotation the body seemed at rest and the stomach quite settled, while the visual field alone whirled rapidly in the direction opposite to that of the previous rotation.
VISION DURING DIZZINESS
BY E. B. HOLT
During and after a prolonged rotation of the head, the visual field seems to spin around before one's eyes,—a phenomenon that is ordinarily called the "dizziness of Purkinje." Delage describes it as follows:[16] "In the experiment of Purkinje, while we are rotating in a positive sense, space seems possessed of a motion in the opposite direction.... This phenomenon is explained by the direction of the nystagmus."