It has appeared that the principal source of scurvy is a vitiated or scanty diet, and that it is very much promoted by cold, moisture, filth, sloth, and dejection of mind. Hard labour has been assigned by some as a cause; but this is not conformable to my observation in general, and what has been related to have happened in the Conqueror[118], more particularly led me to be of a contrary opinion. The principal differences of the symptoms of the scurvy in hot and cold climates, so far as I have observed, are, that in the former the livid hardness on the extremities is an earlier symptom, and in the latter the gums are sooner affected, and the difficulty of breathing is a more frequent and more uneasy symptom. This difficulty of breathing is one of the most fatal symptoms, and is most frequent in those cases in which there are the fewest external marks of the disease, and is probably that form of the complaint which attacks a vital part by a sort of translation from the extremities. There is a remarkable symptom sometimes attendant on this disease which has escaped authors, and is mentioned in Mr. Telford’s Report, page 23. This is the _nyctalopia_, or weakness of the eye-sight, which was also common in the garrison of Gibraltar[119], among those who were affected with the scurvy, a disease that prevailed much during the late siege of that place. With regard to the cure, enough has been said in the preceding parts of this work to prove that fresh vegetables are the most effectual antiscorbutics. I shall here mention a fact farther in proof of this, which has not before been taken notice of. When the fleet arrived at Barbadoes in May, 1781, part of the soldiers, who served as marines, were affected with the scurvy, and being sent to the army hospital, where, at that time, no fresh animal food was allowed, they recovered much faster by being confined to vegetable articles, than the seamen who were fed upon fresh animal food without any fresh vegetables. It has farther appeared, that there is something in a particular class of fruit of the lemon and orange kind, which far surpasses every other remedy, whether dietetic or medicinal. Numberless instances have occurred, in the preceding part of this work, of men having recovered at sea from using the juice of this fruit alone, even under all the inconveniences of a sea diet. When the juice is intended to be kept for a length of time, it should be expressed and bottled, a small quantity of spirits being added to preserve it for if fire is used in preparing it, as in the form of a rob, I know for certain that its virtues will be thereby very much impaired. It is very difficult to say upon what principle these fruits act, for no sensible effects are produced by them except a small increase of some of the secretions.