Hereditary Diseases of Sheep and Pigs. 
27 
violent, manner ; but the nature of those changes, which doubt- 
less occur within the cranium, still remains unexplained, and in 
this instance post mortem examinations do not help us much. 
There is usually more or less softening of the brain ; but some- 
times neither the brain nor any part of the nervous system 
presents anything abnormal. The vascularity of the brain, and 
its engorgement with dark-coloured blood, so much spoken of 
by some authors, depend chiefly on the blood being driven in 
undue amount to the deep-seated organs by the violent contrac- 
tions of the external muscles. But apart from the nervous sys- 
tem, there are often found derangements of other organs, which 
seem frequently connected with the production of the disease. 
Thus, among both sheep and cattle, the third stomach is usually 
filled with hard, dry, and partially-digested food ; in dogs, the 
small intestines are frequently filled with worms ; and in these and 
other animals the lungs and other parts are sometimes studded 
with tubercles. But we know little, if anything, of the manner in 
which these conditions produce epilepsy, nor indeed of the modus 
operandi of plethoi'a, derangements of the digestive organs, 
exposure to cold, or any of the other causes of the disease. These 
appear sometimes adequate to produce the disease among stock 
of untainted pedigree, but always act most certainly and power- 
fully among those inheriting a predisposition to the disease. 
The existence in certain individuals of an inherent predisposition 
to epilepsy, and the transmission of such a predisposition from 
parent to offspring, appear undoubted. The disease is always 
especially frequent and formidable in the progeny of those sheep 
that have themselves been subject to it. One extensive agricul- 
turist informs us that he at one time had it frequently among his 
flock ; that it descended for " several " generations ; but that 
since he sold off the faulty race, and drained and otherwise im- 
proved his farm, he has seen none of it. Most breeders and 
shepherds, though they speak most decidedly of the hereditary 
nature of the complaint, are unable to give much statistical 
information regarding it. The hereditary nature of epilepsy 
when it affects the human species, is now well ascertained. 
MM. Bouchet and Casavielh found that of 110 cases of epi- 
lepsy, 31 were hereditary ; and Esquirol found that of 321 persons 
afflicted with epileptic insanity, 105 were descended from insane 
and epileptic parents.* A hereditary tendency to epilepsy 
cannot, among sheep, be distinguished by any external appear- 
ances. Those prone to it are said to have large, unshapely, 
unsymmetrical heads, with one-half unlike the other ; but such 
characters, though indicating a tendency to epilepsy in man, are 
* Watson's Principles and Practice of Physic. Third Edition, vol. i. p. 637. 
