Williams, Fisher, and Udall: The Spavin Group. 15 
A glance at the cartilage of this tibial bone shows that it was 
extensively diseased (Fig. XIII). The cells are arranged in 
mother capsules and variable in size; near the free surface of the 
cartilage they are greatly modified in structure and arrangement. 
In certain areas the cells are larger (Fig. XIII, E'). The con- 
_ nective tissue between the cells is -increased in amount and 
_ fibrous in character, while normal articular cartilage is of the 
hyaline variety. In places we find a metaplasia of the cartilage 
with splitting of its fibers, in other places the cartilage has en- 
tirely atrophied, bringing the abraded articular surfaces of the 
bones in direct contact. 
The condition and appearance of the bone and marrow in this 
section offers a suggestion to the influence exerted by the giant 
cells (osteoclasts) upon bone resorption. This is the only case 
in which we have been able to demonstrate the presence of such 
cells in large numbers, only a few being observed in case IV. 
In case V, however, they were very abundant both in Howschip’s 
lacunz and in the center of the marrow cavities. Certain parts 
of the sections examined presented areas where no giant cells 
were visible, the marrow cavities were rich in a cellular structure, 
and the bone matrix presented marked indications of resorption. 
The lacunz were misshapen or rounded, some were very much 
enlarged with ‘irregular and poorly defined outlines, others ab- 
normally small: The bone cells in such lacunze were hypertro- 
phied, atrophied, or absent. In the majority of cases noted they 
were present, enlarged, and granular in appearance, their posi-~ 
tion in the bone matrix alone, distinguishing them from neigh- 
boring marrow cells (Fig. XIV). 
While it is generally believed that the osteoclasts exert a 
certain influence in bone resorption we have a case where it 
would seem that resorption was rapidly progressing in their 
absence (Fig XIV). It is difficult to understand just how the 
osteoclasts can bring about such marked changes in the bone 
cells that are deeply situated in the bone matrix; the idea 
suggests itself that the primary change begins in the individual 
cells themselves, those of the trabeculz, as well as in those of 
the Haversian canals. As the bone tissue atrophies it is perfectly 
logical that the Haversian canals should become enlarged. Sup- 
pose in Fig. XIV, for example, that three or four of the bone 
corpuscles continue increasing in size until they occupy a common 
space, and that at the same time this. breaks through into the 
