No abstract

Summary Using 61 rabbits, we made an observation on the papillary reaction. After exposing the surface of the cerebral cortex or the dorsal surface of the midbrain, concentric electrodes were inserted, and the alternative current of 0.5‐5 volt and 60 cycle was given on the pretectal region, the central gray matter and its periphery, the stimulated points amounting to 3,500 in total. The pupillary responses areas were histologically determined afterwards by means of Nissl stain and myelin stain series tracing rabbit's pupillary reflex afferent pathway. The result thereof is as follows: 1. The minimum voltage to cause constrictor response and dilatator response with the alternative current stimulation by needle electrode is 0.5 volt. In certain portions, mere insertion of the electrode produced the responses. Pupillo‐constriction concurred in many cases with blephalo‐ptosis and pupillo‐dilstation with the reopening of eyelids. 2. Wheress the pupillo‐constrictor response area was founs localized in the pretectal region, the posterior commissure, the descending peduncle of the posterior commirsure and the central gray matter, the pupillo‐dilatator response area was lesser delimited, as widely distributed over the whole midbrain as covering. the radiatio optical, pretectal region, posterior commissure and its descending peduncle, tectum, tegmentum and the central gray matter. 3. The stimulation on the dorsolateral archiform fiber system in connection with the optic tract and the tractus sublentifomis (Kuhlenbeck) caused contralateral pupillo‐constricticn and the same was caused by the stimulation on the lateral and medial geniculate body, the latter represen ting the pathway of these two fiber systems and also the pretectal arza (Nucl. praetectalis, Nucl. lentifonnis mesencephali, Nucl. sublentiformis), the locus of termination of the pathway, whereas Area praetectalis lying just adjacent to the lateral surface of the posterior commissure yielded both bilateral and contralateral constriction. 4. Bilateral constriction was producible from the median of posterior commissure; bilateral, homolateral and contralateral constriction from the lateral surface of the posterior commissure; lastly, homolateral constriction from the descending peduncle of posterior commissure, respectively. 5. Regarding the interstitial nuclei, there were obtained both homolateral and contralateral constrictions from Nucl. interstitialis principalis com‐missurae posterioris and Nucl. interstitialis supra‐commissuralis commis‐surae posteroris, while only homolateral constriction was obtainable from the interstitial nuclei located in the lateral part of the descending peduncle of posterior commissure. 6. So far as we could roughly determine the scope of the constrictor nucleus in the central gray matter, a small‐cell group found between fasciculus longitudinalis dorsalis and faxiculus longitudinalis medialis lying in the dorsal part of Darkschewitsch nucleus (Kuhlenbeck) and about 200 μ anterior to the main oculomotor nucleus produced the constricti...

Summary With application of Glees' silver method, modification of Bielschow‐sky's method, on 11 rabbit's brain with intersected posterior commissure, we examined the degenerated axis cylinder of the posterior commissural fibers paticipating in the pupillary light reflex pathway and the terminal degeneration of axis in the constrictor nucleus in order to elucidate the light reflex pathway histologically. 1. The fibers directly connecting the bilateral pretectal nuclei pass through the posterior commissure, and join with the pretectal nuclei by the way of dorsolateral archiform fiber system, ventromedial archi‐form fibers system and tractus sublentiformis (Kuhlenbeck). 2. There is a connection between the descending fibers of posterior commissure and interstitial nuclei (Kuhlenbeck). 3. Constituting the afferent fibers of pupillary light reflex running in the descending peduncles of posterior commissure, there are two routes; namely, the way reaching to the constrictor nucleus by the way of the lateral surface of the central gray matter, and another one reaching to the same by joining with the fasciculus longitudinalis medialis and ascending dorsalad from it. 4. The constrictor nucleus is located between the fasciculus longitudinalis dorsalis and fasciculus longitudinalis medialis, covers about 1200 μ from about 200 μ in front of the main oculomotor nucleus down roughly to the middle of the nucleus anterodorsal way toward the dorsal parts of the same, and is composed of a pair of medium‐sized cell groups on both sides. 5. The efferent pupillary light reflex pathway is assumed to be projected from the constrictor nucleus to the pupillary constrictor muscle by the way of the oculomotor fibers.