148 NEW YORK ZOOLOGICAL SOCIETY. 
cavities are found both in the cancellous portions and in the 
marrow proper; these spaces are generally filled by a semi- 
fluid, mucoid or colloid material. 
The microscopic alterations vary and apparently without direct 
relationship in any instances to the special animal or to the cir- 
cumstance under which the disease developed. Thus in some 
of our cases, though the animal was young, the alterations are 
typically those described by Kaufman and others as the “senile’’ 
type of. osteomalacia. This is sometimes associated with what 
Kaufman also classifies as ‘‘Ecte, reine osteomalacia,” in so far 
as we may rest our diagnosis on the microscopic findings in the 
diseased bone. In our opinion the classification is incorrect and 
the changes represent but stages in the same process, the maran- 
tic or senile type apparently being but a more advanced state. 
Some of the bones show an almost complete replacement of 
the normal marrow tissue by compact masses of cells; small 
round cells, multinuclear giant cells, and large polymorphous 
cells, the elongated processes of which form a supporting stroma. 
Blood vessels, most of them newly formed, are found quite 
abundantly and about them are seen plasma cells. Extravasa- 
tions of blood, with resulting disintegration and pigment deposi- 
tion, are seen commonly. The giant cells are very numerous 
in places and are so distributed throughout the tissue as to closely 
resemble the structure of giant-celled sarcoma (see plate 8, Fig. 
B). As a rule, in these instances the endostium is largely re- 
placed by an incomplete layer of large osteoclasts about which 
absorption of the compact tissue is obviously taking place (see 
plate 5, Fig. A). Absorption of lime salts and removal of the 
organic framework of the bone apparently takes place jointly and 
at the same time. In many of the cases marked lacunar absorp- 
tion is also apparent in the compact tissue. In general, no effort 
toward the formation of new bone or cartilage is to be seen; 
but occasionally areas are found, notably in the epyphyseal ends, 
where nodules of a typical cartilage are being formed (see plate 6, 
Fig. A), but in none is calcification taking place, the processes 
not even extending on to the formation of osteoid tissue. In 
some bones, and these we believe to be taken from the more 
slowly progressive cases or those in which for the time being the 
disease has been arrested, this abnormal marrow has been re- 
placed by a mucoid tissue (see plate 6, Fig. B), which has occa- 
sionally broken down into a fluid, forming the cysts mentioned 
above. Where marrow destruction is so extreme, as in speci- 
mens of this kind, it is difficult to understand how regeneration 
