more evidence of its utility, I employ it without putting the least confidence in its power; nor do I expose myself to the same danger as my friend has done for the sake of an experiment.”  I said, “I believe several scientific persons—­Brocchi amongst others—­have doubted the existence of any specific matter in the atmosphere producing intermittent fevers in marshy countries and hot climates; and have been more disposed to attribute the disease to physical causes, dependent upon the great differences of temperature between day and night and to the refrigerating effects of the dense fogs common in such situations in the evening and morning; and, on this hypothesis, they have recommended warm woollen clothing and fires at night as the best preventives against these destructive diseases, so fatal to the peasants who remain in the summer and autumn in the neighbourhood of the maremme of Rome, Tuscany, or Naples.”  The stranger said, “I am acquainted with the opinions of the gentlemen, and they undoubtedly have weight; but that a specific matter of contagion has not been detected by chemical means in the atmosphere of marshes does not prove its non-existence.  We know so little of those agents that affect the human constitution, that it is of no use to reason on this subject.  There can be no doubt that the line of malaria above the Pontine marshes is marked by a dense fog morning and evening, and most of the old Roman towns were placed upon eminences out of the reach of this fog.  I have myself experienced a peculiar effect upon the organs of smell in the neighbourhood of marshes in the evening after a very hot day; and the instances in which people have been seized with intermittents by a single exposure in a place infested by malaria in the season of fevers gives, I think, a strong support to something like a poisonous material existing in the atmosphere in such spots; but I merely offer doubts.  I hope the progress of physiology and of chemistry will at no very distant time solve this important problem.”  Ambrosio now came forward, and bowing to the stranger, said he took the liberty, as he saw from his familiarity with the cicerone that he was well acquainted with Paestum, of asking him whether the masses of travertine, of which the Cyclopean walls and the temples were formed, were really produced by aqueous deposition from the River Silaro, as he had often heard reported.  The stranger replied, “that they were certainly produced by deposition from water; and such deposits are made by the Silaro.  But I rather believe,” he said, “that a lake in the immediate neighbourhood of the city furnished the quarry from which these stones were excavated; and, in half an hour, if you like, after you have finished your examinations of the temples with your guide, I will accompany you to the spot from which it is evident that large masses of the travertine, marmor tiburtinum, or calcareous tufa, have been raised.”  We thanked him for his attention, accepted his invitation, took the usual