Hereditary Diseases of Sheep and Pigs. 
31 
much pain, swelling, and lameness. It attacks animals of all 
ages ; but lambs, from their inability to withstand intense cold, 
are o;enerally most severely affected. Among sheep the disease 
usually owes its production in great part to the operation of 
external or exoteric causes, as being exposed to cold and rain, 
or lying on damp, undrained ground. Indeed, whenever rheu- 
matism occurs, it is a certain evidence of the want either of 
effectual shelter or of sufficient drainage. But these exciting 
causes often receive most active co-operation from congenital 
predisposing causes. The nature of such congenital causes is 
unknown, but their existence is often indisputable. It is well 
ascertained that when rheumatism has once occurred it is very 
apt to occur again, owing, we believe, to some peculiar altera- 
tion of tissue induced by the first attack. Now, it is, we think, 
some such altered condition of tissue, transmitted from one 
generation to another, which constitutes a hereditary tendency to 
the disease. Indeed, in the human subject, as well as in cattle, 
rheumatism is now generally admitted to be hereditary ; and 
since in sheep the disease is in every other respect the same, we 
are surely justified in pronouncing it to be hereditary in them 
likewise. Care must therefore be taken to avoid for breeding 
purposes all sheep that have been subject to rheumatism, and 
also those with lank ungainly forms, long unsymmetrical limbs, 
large coarse joints, and other marked indications of predisposi- 
tion to the disease. 
Scrofida frequently occurs among sheep, presenting itself 
under several different forms, and predisposing to a great many 
diseases. In sheep of a strumous or scrofulous constitution or 
habit of body, the blood is not properly elaborated, and contains 
an excess of albumen, with a deficiency of red corpuscles and 
fat, and forms a loose and soft coagulum. During ordinary 
nutrition, but more particularly during inflammation, it is apt 
to deposit, especially on free mucous surfaces, a peculiar non- 
organisable matter termed tubercle — a substance of a yellowish 
white, opaque, granular, often cheesy appearance, and consisting 
of variable proportions of albumen, a little fatty matter, and 
salts chiefly of lime. Wherever the most minute speck of such 
tubercular matter is precipitated from the blood, it is very apt 
to increase in size by continual accretion. The form of the 
deposit is moulded by the interstices of tissues with which it 
is in contact ; but, when not pressed on, its form is undeter- 
minate. It is not subject to any vital changes, and is incapable 
of organisation, but often becomes, after a time, hard and grittv, 
from the removal of its more fluid and organic parts. In contact 
with vascular tissues, it is very apt to induce much irritation 
and inflammation, accompanied by unhealthy effusion and the 
