It seems to be the chersydros which Dante alludes to in the following verses:
“Come le rane innanzi alla nemica
Biscia per l’acqua si dileguan tutte,
Finch’ alla terra ciascuna s’ abbica.”
Inferno, canto ix.
For an account of the hydrus, see [the sixteenth section].
According to Sprengel, the dryinus is the coluber lebetinus. (Notæ in Dios.)
Agricola finds fault with Lucan for distinguishing the chersydros from the hydrus or natrix. He remarks that the boa is a species of hydrus. (De Anim. sub.) They are now generally held to be different. See, however, our commentary on [the sixteenth section].
SECT. XV.—ON THE HÆMORRHUS, PRESTER, OR DIPSAS.
Those bitten by the hæmorrhus experience violent pains, and both longitudinal and lateral contractions of the porous parts of the body, occasioned by the persistence of the pains. From the bite there is a copious discharge of blood, and if there happen to be a sore on any part of the body it bursts out and discharges blood. The alvine evacuations likewise are bloody, and the blood which is evacuated is thrombous. When they cough they bring up blood from the lungs, and they die at last vomiting blood irremediably. Those bitten by the dipsas experience intolerable heat and intense thirst which is insatiable and unceasing, so that they swallow copious draughts, and yet they feel as if they had never drunk; and the whole system is affected, as in dropsy, owing to constant ingestion of drink. Hence the animal has been called prester, causon, and dipsas. By most of the ancients those bitten by the hæmorrhus and dipsas were given over as incurable. But if we have no particular remedies for this reptile we ought to make trial of the general applications, and immediately have recourse to scarifications and burning, and, if the part permit, to amputation of the extremities. Then acrid cataplasms may be applied. All kinds of acrid food are also useful, especially that from pickles, drinking undiluted wine, and using baths. These things are to be applied perseveringly, and repeated at short intervals, before the complaints make their attacks; for after they make their appearance no advantage can be derived from medical aid. We find these topical remedies described for their bites, namely, for those of the dipsas, the powdered leaves of purslain with vinegar, polenta, and bramble leaves powdered with honey, plantain, hyssop, white garlic, leeks, rue, and nettle; and for those of the hæmorrhus the same things, and, in addition, boiled vine leaves triturated with honey. By the mouth the burnt head of the animal itself may be taken in a draught, or garlic with oil of iris. They may likewise eat dried grapes.