HEREDITARY DISEASES OF HORSES AND CATTLE. 157 
quently it is not disease itself which is transmitted, but organs 
or textures of such imperfect kind, that they are liable to be 
morbidly affected by causes which would produce no effect 
on limbs or textures soundly and normally developed. 
Regarding the subject of hereditary diseases in a general 
way, we shall have to consider — 
i. Those which are induced by peculiarity of conformation , both 
in the external and internal parts of the body . 
n. Those in the transmission of which the condition of the blood 
may be supposed to be partly or wholly concerned. 
In treating the subject under these two heads, we shall 
follow the classification as closely as possibly, but, on account 
of the close and intimate connexion existing between the 
solids and the fluid portions of the body, in growth, function, 
and change, there will be a difficulty experienced in some 
instances, in separating them in the inquiry. Our first 
example will afford an instance of the kind. 
I. (a.) Spavin and other Ossific Enlargements — -the predispo- 
sition to which may be either constitutional or local. They 
are composed of the earthy matters of bone, chiefly invading 
the tissues low in the scale of organization, such as cartilage 
and fibro-cartilaginous substances; injuring the structure 
and functions of the parts, by rendering them rigid and in- 
elastic, and causing partial or complete lameness, depending 
on the situation and the extent of the deposition. 
It is perfectly well ascertained that the progeny of some 
horses inherit a constitutional tendency to splints, spavins, 
ring-bones, and other bony deposits, without exhibiting any 
peculiar conformation of limbs or joints to account for it. 
These are instances of an ossific diathesis , transmitted from 
parent to offspring. But, on the other hand, this hereditary 
predisposition more commonly depends on faulty or peculiar 
conformation. 
Thus horses most disposed to spavins are those possessing 
short pointed hocks, deficient in width and breadth below, 
and disproportionately small compared with the upper portion 
of the joint. Those most disposed to ring-bones are horses 
with upright pasterns and high action ; and those most liable 
to ossified cartilages are the heavy draught breeds ; so much so 
that it is not an uncommon case to find the cartilages of the 
with the mother, owing to their contaminating influence, or their extension 
throughout her organization, are not, properly speaking, hereditary 
The following case is more to the purpose, related by the late Mr. Robert 
Reed, Crediton, Y.S. — “ I have seen , 55 he says, “ a foal born blind, having 
a lenticular cataract in each eye, from the dam having been put to a 
stallion with a cataract in each eye, the result of a constitutional inflam- 
mation.” 
