It is difficult to ascertain how far the influence of vapours from woods and marshes extend; but there is reason to think that it is to a very small distance. When the ships watered at Rock Fort, they found that if they anchored close to the shore, so as to smell the land air, the health of the men was affected; but upon removing two cables length, no inconvenience was perceived. I was informed of the following fact, in proof of the same, by the medical gentlemen who attended the army in Jamaica:--The garrison of Fort Augusta, which stands very near some marshes, to which it is to leeward when the land wind blows, was yet remarkably healthy; but it became at one time extremely sickly upon the breaking in of the sea in consequence of a high tide, whereby the water which was retained in the hollows of the fort produced a putrid moisture in the soil, exhaling a vapour offensive to the smell, and with all the noxious effects upon health commonly arising from the effluvia of marshes. [41] Dr. Hendy has lately published an ingenious treatise upon this disease. [42] See Sydenham’s Works. [43] See Part I. Book II. Chap. VI. [44] We have a proof of this fact in particular, in the account of the jail distemper, which broke out at the Old Bailey in the year 1750. [45] See Martin’s History of the Western Islands, and Medical Communications, Vol. I. page 68. [46] There are some contagious diseases which cannot be propagated but by their own peculiar infections, as has been before observed, just as the seeds of vegetables are necessary to continue their several species; so that if the infectious poison were lost, so would the disease. Of this kind are the small pox, and the other diseases to which man is subject but once during life. There are other diseases which produce infection without having themselves proceeded from it. Of this kind are fevers and fluxes.