28 
Hereditary Diseases of Sheep and Pigs. 
of less value among sheep, for in the case of the latter animals 
they are sometimes present where there is no tendency to the 
disease, and sometimes absent where the tendency is undoubted. 
Sturdy, turnsick, or hydatids in the brain, used to be very- 
prevalent in this country, but is now chiefly confined to localities 
as yet unreached by modern improvements in ajjriculture and 
reforms in the management of stock. It is rarely met with where 
tlie land is dry, and the flocks well tended and fed. Youatt * 
and other writers seem to view it as directly hereditary ; but this 
is very improbable, and is not borne out by careful observation. 
Sheep affected by the disease do not produce lambs exhibiting 
any unusual proclivity to it ; but as it most frequently affects 
animals of a weak and depraved state of body, and as such states 
of body are notoriously hereditary, the disease may rather be 
considered as hereditary from indirect causes. 
Chronic diseases of the respiratory oryans are generally accom- 
panied by some alteration of structure which has assumed a 
hereditary character. This is often the case with the irritable 
condition of the bronchial mucous membrane, which gives rise to 
chronic couyh. This affection is of frequent occurrence among 
sheep, is attended with so much irritation as sometimes to pre- 
vent the animal from thriving, and occasionally leads to inflam- 
mation of the lungs. It is always much aggravated during wet 
or changeable weather. Sheep with narrow throats and chests, 
and of a consumptive constitution, are most commonly predis- 
posed to chronic cough. We might here consider pulmonary 
consumption as one of the hereditary diseases of the respiratory 
organs, but shall postpone its notice until we come to speak of 
scrofulous complaints. 
Some of the diseases of the digestive orya)is of sheep are apt to 
owe their production in part to the action of hereditary causes. 
This is particularly the case with diarrhoea and dysentery, which 
are especially frequent and severe among animals of a spare 
lank form, with flat ribs, much space between the prominence of 
tlie haunch- bone and the last rib, angular quarters, and badly 
set-on tail ; dark, scurfy-looking skins, and soft, flabby, muscular 
systems. In such sheep the intestines are weak, and apt to suffer 
even from the slightest disturbing causes. Exposure to wet or 
cold, or sudden alterations of food, speedily determine a trouble- 
some diarrhosa. This is especially apt to occur during spring 
and autumn, particularly in lambs, amongst which it frequently 
causes considerable mortality. We are apt to entertain very 
vague ideas concerning this common and simple complaint : it is 
usually produced by some irritant matter either introduced into 
* Youatt on Sheep (Library of Useful Knowledge), pp. 381, 382. 
