1. A droplet application of adrenaline, ephedrine and adrenalone in the concentrations of 0.01%, 0.5% and 1% respectively applied to the pupil of normal rabbits brought about mydriasis of a similar degree in every case. Consequently, the potency of these drugs on bringing about mydriasis was in the order of 100:2:1. This finding coincides well with that of Kinoshita and Tani of our labaratory in which they found that ephedrine and adrenalone hardly affected the accelerative fibers of the sympathetic nervous system but these drugs strongly influenced the inhibitory fibers. The fact that the mydriatic action of ephedrine and adrenalone is far less potent than that of adrenaline seems to be explained by the fact that the dilatator muscles of the pupil are innervated with the accelerative fibers.
2. In the rabbit given a monolateral resection of the superior cervical ganglion the pupil on the resected side responded much more sensitively to these three drugs than that on the normal side. In such instances, there can be observed the so called “Paradoxe Pupillenerweiterung” phenomenon.
3. The administration of yohimbine alone has hardly any effect on the pupil of both normal and monolaterally resected rabbits, but in the rabbits previously treated with yohimbine, the mydriatic effect of adrenaline is clearly diminished. This fact further supports the contention that the accelerative fibers of the sympathetic nervous system are the principal controller of the dilatator muscles.
4. Urethan is found to enhance the mydriatic effet of adrenaline in both normal and rabbits monolaterally resected of superior cervical ganglion, but a similar phenomenon can also be observed in the rabbits given adrenalectomy. Therefore, it seems that the enhancement of adrenaline mydriasis induced by urethan is not due to the increase in the adrenaline secretion but rather due to the paralysis of the cerebral cortex.