578 
DISEASE OF OSSEOUS TISSUE IN THE HORSE. 
When a thin section was examined with the microscope, it presented the 
appearance delineated at Fig. I (section taken from the outer surface, and 
middle portion, of the left jaw-bone). 
The osseous tissue is seen to be expanded into a network of fine fibres 
(Fig. I, a). The Haversian canals(Fig\ I, b ), on the other hand, have become 
so enlarged that, at first sight, they might be mistaken for the bony tissue, 
and the bony tissue mistaken for the Harversian canals. On examination 
with a higher power, not only is the osseous tissue seen to be rarified, but 
tlie canaliculi proceeding from the lacunae, or bone-corpuscles, as they were 
formerly called, are, in many cases, obliterated. The lacunae (Fig. I, c ) them¬ 
selves are also not so distinct as in healthy bone. The enlarged Haversian 
spaces are tilled with a gelatinous matter (Fig. T, d), mingled with a small 
portion of fat, and here and there pervaded with fine, scarcely visible fibres. 
2d, Long bones of the extremities.—The periosteum, although readily 
detached, does not come away with so much facility as from the bones 
of the head, except towards the ends of the bones, where, strange to 
say, the ligament had become detached by the mere movements of the animal 
during life. The outer surface of the shaft of the bone is firm enough, but 
on section it is found to be greatly thinned, in consequence of an enlarge¬ 
ment of the medullary canal having taken place at the expense of the osseous 
tissue. 
The dilatation of the medullary cavity is most marked towards the extre¬ 
mities of the bone, and there the marrow is deeply tinged with blood. The 
osseous tissue which, in some parts, is reduced to one half, or even one third 
of its normal thickness, does not present the spongy characters of the cra¬ 
nial bones ; but, on the contrary, is dense, and so hard that it cannot be cut 
with a knife. 
After the calcareous matter is removed by acid, the section of the animal 
matter has a somewhat glistening, cartilaginous appearance, here and there 
dotted witli opaque, white spots. Under the microscope, a thin section 
reveals a curious condition of things. The Haversian canals, as w r ell as the 
concentric bony lamellae surrounding them, appear perfectly normal (Fig. 
II, a). The lacunae and canaliculi, as far as can be ascertained in the de¬ 
calcified bone, are equally healthy. But, on close inspection, the opaque, 
white spots, observed by the naked eye, are seen to be irregular-shaped 
cavities in the osseous tissue, filled with fat-cells (Fig. II, b). These cavities 
vary in size, from that of a pin’s point up to a millet seed. They are not 
limited to any particular portion of the osseous structure, although they 
seem to have commenced, for the most part, in the lacunae. Some however 
may, with equal truth, be said to have originated in the Haversian canals, the 
walls of which have been gradually broken down, and eaten away, as the 
morbid condition advanced ; the place of the earthy and animal matter being 
gradually taken up by fat-corpuscles. Fig. II shows this state of bone very 
clearly. The condition of the cartilages and other tissues I need not allude 
to, as you are familiar with them. 
Any additional information I shall be happy to furnish you with, if such 
be in my power. 
Please return to me the sketches, when you have done with them. 
I remain very faithfully yours, 
George Harley, M.D. 
To G. Varnell, Esq. 
The bones, after being macerated and dried, exhibited 
many peculiarities which were not apparent in their fresh 
