16 Williams, Fisher, and Udall: The Spavin Group. 
neighboring marrow cavity; such changes would result in the 
formation of a Howschip’s lacuna. 
Summary. — This group of: diseases is characterized by an 
inflammation of the bone, cartilage, and capsular ligament. The 
following changes are noted in the bone: hypertrophy of the 
marrow cavities, and atrophy of the osseous matrix. The mar- 
row cells are greatly increased in numbers. The bone cells 
(corpuscles) become granular in appearance and smaller in size. 
The lacune are enlarged, and at the same time may lose their 
typical form. The canaliculi undergo partial or complete atrophy. 
The disease process seems to be operative throughout the whole 
’ extent of the affected -area at the same time; that is, bone 
resorption is not confined to those portions of the osseous matrix 
with which the marrow cavities are in direct contact (osteo- 
myolitis), but progresses just as rapidly within the interior of 
the compact bone (ostitis). These changes are found in the 
bone during the earlier and more active stages of the disease 
(osteo-porosis). They are demonstrated in figures XI, XII, XIII, 
and XIV. During this stage the bone is abnormally soft, porous, 
and light (osteo-porosis), later becoming more compact and 
heavier (osteo-sclerosis). The histological characteristics of 
osteo-sclerosis (condensing ostitis) are atrophy of the marrow 
cavities and hypertrophy of the bone matrix; the-cellular struc- 
ture of the marrow cavities becomes greatly increased in amount 
(Figs. XI and XIII). There is a cessation of the inflammatory 
process; and resorption of bone is replaced by a regeneration of 
the osseous structure. Many of the lacunz, however, fail to 
regain their lost bone cells (Fig. X, d). The disease of the bone 
has been accurately termed: ‘“‘ Osteo-porosis succeeded by os- 
teo-sclerosis’’ (Gotti, Bayer, Frohner, Eberlein, etc.). 
The characteristic changes in the cartilage are: fibrillation of 
the superficial layers, extending in some cases to the osseous 
tissue; hypertrophy of the intercellular matrix, as well as hyper- 
trophy and proliferation of the cartilage cells; partial or com- 
plete atrophy of certain portions of the articular cartilage charac- 
terized in some cases by the formation of ulcer-like depressions 
(Figs. XII and XIII). 
The capsular ligament presents the most pronounced changes 
in those articulations of which the knee joint is a type. In cer- 
tain cases, especially in the earlier stages of the inflammation 
caused by this disease, the capsular ligament is distended with an 
