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50.

The pupil did not seem to me a sufficiently typical object for the determination of this all important point and I, therefore, concluded to try the bloodvessels, more especially, since it is now looked upon generally, as a well settled question in physiology that the bloodvessels are supplied by two kinds of nerve-structures namely vaso-motor and vaso-inhibitory or dilator, the stimulation of the former causing vaso-constriction, that of the latter giving rise to vaso-dilatation.

Cosequently, we might argue that tropic acid is that part of the molecule of atropine which causes pupillary dilatation and if we have, furthermore, reasons to believe, that tissues which are identical both in histological structure and physiological function, are also similarly affected by the same chemical stimuli, then it ought to follow that this same portion of the molecule of atropine should