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CHAP. XV. Of Diseases of the glassy Humour.
THE glassy Humour is placed under the Cristaline, and is therefore made by Nature clear, that the Spe∣cies may be conveyed pure and clear to the Optick Nerves; if therefore the perspicuity of it be sullied by the mixture of any Humour, and it become dark, the Sight is more or less diminished, proportionably to the degree of dark∣ness of it.
Moreover, this Humour may be injured by being mis∣placed, namely, if part of it by a Blow or Contusion is thrust before the Cristalin Humour; for then the Sight is darkned, for the glassy humour is thicker than the watry, and so the Species of Objects cannot be brought pure and sincere to the Cristaline Humour.
The former of these Diseases can be known by no Signs; but be imagined only by reason: For this Humour cannot be seen, nor the disposition of it known; therefore Pra∣ctitioners, when they perceive no fault in the Eye, con∣found this with the Gutta Serena, and that without any damage to the Patient; for extraneous Humours poured upon the glassy Humour must be discussed by the same Remedies wherewith a Gutta Serena is wont to be Cured. But the vitiated situation of the glassy Humour may be known, by appearing like the White of an Egg under the Pupil; but it cannot be distinguished from a suffusion, unless the antecedent and procatarctick causes are well considered; for a suffusion proceeds from a simple influx of the Humours: But this from the glassy Humour misplaced by a Blow or Wound.
This Disease is incurable by Art: But sometimes it hap∣pens to be Cured by Nature; and therefore the whole business is to be left to her.