It is a singular, but well ascertained fact, that the miasmata lose their noxious properties by passing over even a small surface of water. Probably they are absorbed by it. Many instances have been related, where some of the crew of a ship have landed on a malarious coast, and have all been attacked by the fever, while the rest of the sailors who remained on board, continued all healthy and well, though the ship was close to the shore. Some writers are of opinion that, owing to this property of water of absorbing the poison, the disease may be conveyed by drinking the said water, and certainly some cases reported show very strong grounds for such a belief.

Dr. and Mrs. Evans, of Bedford, were both attacked with Ague while staying at Versailles in the year 1845. The water used there for domestic purposes is brought from the Seine at Marli. A large tank in which it was collected for distribution to a particular quarter happened at that time to be damaged; and the mayor of the place provided a new supply of water, consisting of the surface drainage of the surrounding country, which is marshy. This water the inhabitants of Versailles would not drink; but Dr. and Mrs. Evans, living at a hotel, drank it unwittingly. It was made use of by a regiment of cavalry also. The result was that they who drank the water suffered intermittent fever of so severe a type that seven or eight of the soldiers died in one day. Upon careful investigation, it was ascertained that those only of the troops were attacked who had drunk the marsh water, all the rest, as well as the towns-people, having escaped, though all of them breathed the same atmosphere.

Another remarkable property of the marsh poison is its attraction towards, and its adherence to the foliage of lofty umbrageous trees, so that it is very dangerous, in malarious places, to go under large thick trees, and still more dangerous to sleep under them. But this property, thus a source of peril to those who are ignorant of it, affords when known and rightly made use of, a mode of protection and remedy against the influence of the miasmata. In the territory of Guiana, where large trees abound, the settlers live fearlessly, and unhurt, close to the most pestiferous marshes, and to leeward of them, provided that a screen or belt of trees be interposed. New Amsterdam, in Berbice, lies on the lee side of an immense swampy forest, in the direct track of a strong trade-wind that blows night and day, and pollutes even the sleeping apartments of the town with the stench of the marshes, yet it brings no fevers. The inhabitants are well aware that it would be almost certain death to a European to sleep, or even to remain after nightfall, within the verge of the forest. To cut down the trees would not only be a perilous operation in itself; but would let in pestilence on the town.

Among the circumstances which predispose to Ague, debility has a powerful influence. It is important to be aware of this, as it concerns the treatment and the management of the patient after the disease has been subdued. Soldiers have been exposed to the exciting cause, without being affected by it, while strong and in good health; and have fallen ill of intermittent fever upon being weakened by exertion and fatigue. I have known a gentleman who lived in Canada for forty-two years without getting Ague; and at length, on some accidental exposure when recovering from some indisposition, was immediately attacked with Ague.

But the strongest predisposing cause of all is a previous attack of the disease itself. The effect of former attacks upon the system is such, that the complaint may be reproduced by agencies which under any other circumstances would be quite harmless for exciting Ague. If a person were never exposed to the malaria, he would never have Ague; but having once had Ague, he may many times have it again, although he should never again be subjected to the direct influence of the malaria. The late Dr. James Gregory, of Edinburgh, had a brother-in-law who illustrated well in his own person the effects of predisposing circumstances in respect of Ague. This gentleman was a strong, active man, and commanded a battalion in the West Indies: and he escaped for a long time, while others were falling down around him in remittent fever. At last he was wounded by a musket-ball, which passed through his shoulder. He insisted, much against the will of the Surgeon of the regiment, on resuming his duties before his strength was completely restored; and the consequence was that he was immediately attacked by a remittent fever of such violence, that his life was for some time despaired of. But this was not all. The remittent disease assumed by degrees a distinctly intermittent form, and became a tertian: and at last he got well and strong, and returned to England. Yet, for a long while, though to all appearance his health was re-established, ague fits would from time to time occur; and they came precisely at the day and hour on which they would have happened if the tertian had continued with its original type; and slight causes were sufficient to reproduce them. He had marked, in an almanac, the days the fits were expected; and on those days it recurred for some time, whenever the East wind blew. This very circumstance, the East wind, is a common exciting cause in such cases; exposure to damp cold in any way is another.

When persons having intermittent fever are unable to leave the unhealthy situation in which they have been exposed to the influence of the malaria, and especially when they are placed under unfavourable circumstances in respect of food,clothing and shelter, the disease is apt to become exceedingly serious, leading to disorder of the sensorium, and great disturbance of the digestive organs, even in the intermissions; sickness, diarrhoea, dysentery, disease of the liver. In Zealand, the biliary functions suffer so much during the complaint, that it is commonly known among the inhabitants of that country under the name of the gall fever.