2. What is the nature of stiff pupils? A pupil is called stiff in the sense of the Argyll-Robertson pupil if it fails to react to illumination either of itself or of the other eye and at the same time if it reacts properly in convergence and accommodation. Of course the stiffness of a blind eye must not be regarded as an Argyll-Robertson pupil. In a case of right-sided Argyll-Robertson pupil, therefore, the left pupil reacts properly both to direct illumination of itself and to illumination of the right eye, but the right eye fails to react to illumination of either eye. Such an Argyll-Robertson right pupil will remain of the same width both in darkness and in light. Clinicians agree that the Argyll-Robertson is diagnosticated rather too frequently than too seldom, and this by reason of the fact that a sluggishness of light reaction is interpreted as stiffness. The sign, as is well known, has come to be regarded as almost pathognomonic of tabetic or paretic neurosyphilis. Nonne, however, has found among 510 cases of alcoholism, nine instances of Argyll-Robertson pupil and 19 cases of sluggish light reactions. The pathological anatomy of this sign is still doubtful although a number of schematic accounts are available; among hypotheses, one may think of an elective effect of the tabetic or paretic degeneration upon reflex collaterals. The explanation would then resemble that for absent knee-jerks and kindred reflex disorders. We should then hypothesize a loss of the finer processes of the terminal arborizations about the cells of the nucleus of sphincter nucleus iridis. However, the situation of the sphincter iridis has not yet been absolutely determined. When a pupil is said to be entirely stiff it means that it reacts neither to light nor accommodation. This condition not infrequently follows the partial stiffness or Argyll-Robertson reaction. 3. Is the Argyll-Robertson pupil more tabetic than paretic? This has been claimed at times, but in point of fact, the Argyll-Robertson pupil is very frequent in paresis, and so also are posterior column changes. According to statistics of Bumke, 36% of tabetics fail to show the Argyll-Robertson pupil, and 38% of paretics. When, however, finer methods, such as those standardized by Weiler, with photographic records, are employed, the number of cases without at least a tendency to the Argyll-Robertson pupil becomes much smaller. In connection with the important question as to the classical Argyll-Robertson pupil and pupillary sluggishness to light, it may be inquired what are the ocular signs in neurosyphilis? Joffroy has tabulated the signs in 300 general paretics as follows: