22 
Hereditary Diseases of Sheep and Pigs. 
consumption, or rheumatism ; as also all those afTectcd by any 
disease depending upon structural change of any part or tissue. 
Accidental and acquired diseases or deformities are less apt to be 
propagated than those Avhich are congenital or inherent ; but, 
like external peculiarities, they do sometimes become perma- 
nently hereditary, and hence it is usually safer and wiser also to 
discard animals so affected. 
When it is desired to breed from any animal which, though 
recommending itself by superior general qualities, has neverthe- 
less some slight defect of symmetry, or some faint tendency to 
disease (for which, however, scarcely any good qualities can, we 
think, sufficiently compensate), it should be mated with an 
animal which is super-excellent in every respect in which it is 
deficient. On no account should any animal of doubtful per- 
fection, or suspected soundness, be allowed to breed with one 
near of kin to it ; for in the great majority of such cases both 
parents will have similar imperfections and faults, which will 
appear in the offspring in a far more prominent and aggravated 
form than they existed in either parent. 
The rearing and general management of animals having a 
hereditary tendency to disease also requires unusual care ; for 
such animals are very apt to suffer from all influences inimical 
to health. In them ordinary causes of disease operate speedily 
and powerfully : common and simple disorders are apt to urge 
on the hereditary predisposition to actual disease, and after- 
wards to become themselves absoi'bed into the malady they have 
produced ; while remedial measures act only imperfectly and 
palliatively, for they cannot of course remove the morbific ten- 
dency — the fons et origo of the malady. Such tendencies can 
only be effectually eradicated by crossing not only the animal 
itself, but also its offspring for several generations Avith perfect 
and healthy stock. Nor must the breeder be misled by the dis- 
appearance of any defect or disease during a single generation, 
for a tendency to disease often remains latent for one or even 
two generations, and then reappears with all its pristine force. 
This is often illustrated by consumption, epilepsy, and indeed 
by all hereditary diseases, and also by hereditary peculiarities of 
shape, or colour, which, like diseases, often skip over one or 
two generations, and then reappear. Tliis phenomenon is techni- 
cally called stadisin, and the offspring are said, in the language 
of many breeders, to call hack to their grand parents or other 
more remote ancestors. 
In order to maintain stock, whether horses, cattle, sheep, or 
pigs, in perfect symmetry and free from all defects and diseases, 
it is absolutely necessary to prevent the females from being put 
to any male having qualities that are to be avoided, for the 
