9. Bell, in his treatise on surgery, speaks of a kind of tumour, at first soft, membranous, and adhering to the internal surface of the capsule, but which, according to him, may become afterwards hard and solid, and be detached so as to float loose in the joint. But are not these tumours different in their nature from those destined to be converted into bone? Do they, in fact, ever undergo the changes mentioned by Bell? Desault having never met with any of them, was unable to offer an opinion on the subject. In the mean time, an observation made by Monro, may serve to throw some light on the question: he once saw, in one of these productions, a cellular nucleus surrounded by a covering of bone. 10. Though usually simple and free from complication, this affection may, according to some authors, give rise occasionally to a dropsy in the joint. Pare is the first who has made mention of this: he found one of these bodies in a patient’s knee, into which he had made an incision for the purpose of drawing off a collection of water. Simson, on extracting a similar body, gave vent to four ounces of water. But, as on the one hand, a dropsy of a joint oftentimes exists without these foreign bodies; so, on the other, these bodies are almost always found disconnected from dropsy. Nor is there any affinity between the acknowledged causes of an accumulation of synovia, and the presence of these bodies; so that when the two diseases do exist together, it is altogether probable, that they are independent of each other. § III. OF THE CAUSES. 11. The formation of articular concretions succeeds frequently to blows or falls received on the joint, in which case, a swelling more or less considerable in the surrounding soft parts, showing itself from the first, and remaining for some time, at length allows the foreign body to be perceived, and does not, in general, disappear during the continuance of the body in the part. 12. Sometimes no external injury contributes to the formation of the body, and then, a spontaneous swelling precedes its detection, as Desault observed in two patients, where nothing was known to have concurred in the production of the disease. Constant rest increases this swelling, while exercise and a temperate mode of life diminish it. 13. But what can be the immediate cause of these tumours? Are they, as some allege, an aggregation or crystallization of particles of matter conveyed into the interior of the joint by the synovia, in the same manner as the rudiments of a stone are conveyed into the bladder by the urine? Their organic appearance and the vessels that pervade them, are unfavourable to such an opinion. Can they be, agreeably to the conjecture of Theden, articular glands bruised by means of strokes or falls? Or are they, as some authors will have it, portions of the cartilage of the joint, detached by the same causes? How then will their spontaneous formation be explained?