But why trouble ourselves about the cause, provided we can remedy the effects? Nature conceals from us the means, and discloses to us nothing but the results. Theories are fluctuating; but experience is still the same: let us search, then, by an attention to facts, for that which we cannot learn from first principles. § IV. OF THE SIGNS. 14. The phenomena which announce the presence of foreign bodies in the joint of the knee, are sometimes clothed in a character of such evidence, that they cannot be mistaken; at other times, the nature of the disease eludes the most accurate researches: the cause of this variety may be easily perceived. As the joint presents different depressions and eminences, and as the bodies, being usually loose and detached, may travel through its whole extent, they produce different effects, according to the particular situations which they occupy. If lodged in a depression, they are not compressed, and cannot, of course, give rise to any troublesome affection. If they bear on an eminence, such as the condyls, or the posterior part of the rotula, they are forcibly compressed, and must derange, in some measure, the functions of the joint. Hence the precise nature of the affection cannot be at all times derived from the state of the symptoms. 15. Sometimes the patient can stand and walk with perfect freedom and ease, while, at other times, a sudden pain seizing him, obliges him to sit down, or even causes him to fall, if there be nothing at hand to support him. This pain subsists for a longer or shorter time. One motion produces it, and sometimes another, made in an opposite direction, removes it. But in common it is of some continuance, and then the patient is obliged to keep his bed. 16. If the state of the joint be examined, it will be found more or less swollen, when the pain is very acute. When the pain ceases, the swelling in part disappears. It is never sufficient to prevent the fingers, when drawn along the external surface of the joint, from discovering the presence of the foreign body, when it forms a protuberance under the integuments. It is then found sometimes above the rotula, by the side of the tendon of the extensor muscles, and that is the place where it usually produces least pain; at other times, it is lower down, in front of the condyls, and by the side of the rotula. It is occasionally found immediately behind the tendon of the extensor muscles; in this case so acute is the pain, that the patient is generally unable to stand. But it is when it is situated behind the rotula, near to the projecting ridge which runs across its posterior surface, that it gives rise to the most serious affections.