thinned, and friable (osteoporosis), so that it has been easily cut or crushed, and it is frequently loaded with fat. True ankylosis of the diseased joints is rare, except in the very small articulations when kept at rest; even under this condition fibrous ankylosis is not of frequent occurrence. [Footnote 228: _Illustrations of the Effects of Rheumatic Gout_, London, 1857.] [Footnote 229: Forster, _Handbuch der Path. Anat._, p. 1000.] [Footnote 230: _Virchow's Archiv_, 1877.] Finally, the interarticular fibro-cartilages and ligaments and the long {88} tendon of the biceps degenerate and are absorbed. The muscles in protracted cases suffer simple atrophy, but are sometimes the seat of an interstitial accumulation of fat. Thus far, no lesions of the nerves supplying the diseased joints nor of the spinal cord have been discovered. ETIOLOGY.--The causation of rheumatoid arthritis is involved in much obscurity--in part, because sufficient attention has not been paid to its clinical varieties. We will examine first the general progressive form which is the more common. In women it prevails during the child-bearing period. It is probably oftenest developed between twenty and thirty, and continues to occur frequently up to the period of the menopause, fifty, after which it develops comparatively seldom. Of Ord's 33 cases, 10 were between twenty and thirty years; 11 between thirty and forty; 9 between forty and fifty; and 3 between fifty and sixty.[231] Children are not exempt. E. C. Seguin saw three children of the same family suffering from the disease at ages from two and a half to four years.[232] Moncorvo[233] met with an example at two years and a half, Laborde at four, and Charcot at ten. It occasionally begins in both sexes after sixty. [Footnote 231: _Brit. Med. Jour._, 1880, 156.] [Footnote 232: _The Med. Record_, London, 1877, 797.] [Footnote 233: _Du Rheumatisme Chronique Noueux des Enfans_, Paris, 1880.] It is pre-eminently a disease of females up at least to fifty; after that it is not infrequent in men, and is then often only partial, at least at first. The most frequent progressive form, however, does often occur even in boys. It is probably more frequently observed in cold and damp climates than in those of opposite qualities, for cold is regarded as its most common cause. However, it is met with in India and other hot climates. Besnier asserts it is almost unknown in the tropics, but new investigations are needed on this point.