Hereditary Diseases of Sheep and Pif/s. 
25 
after a few generations fixed and permanent and almost incapable 
of beino- eradicated. In noticing the more important hereditary 
diseases of slieep, Ave shall endeavour to indicate, as fully as our 
limited space will permit, the nature and symptoms of these 
diseases, and also, so far as is known, the external and visible 
signs which indicate a predisposition to them. Such signs 
should especially be noted by breeders, as enabling them to 
detect defects and predispositions to disease which otherwise 
could be discovered only by a knowledge of the animal's 
pedigree. 
In discussing this head we shall adopt the following arrange- 
ment : — Diseases of the brain and nervous system ; diseases of 
the thoracic and abdominal viscera ; rheumatic and scrofulous 
affections ; and general faults and vices of external form. 
Tliere are several diseases of the brain and nervous system 
which are decidedly hereditary in all animals. Amongst the 
more highly improved breeds of sheep, many individuals, usually 
distinguished by their square and compact forms and soft pliant 
skins, are able to manufacture in a short time large quantities of 
blood. In favourable circumstances they carry on this process 
more rapidly than the wants of the system require, and thus get 
speedily into high condition. But this valuable tendency to 
assimilate food readily, and to grow and fatten with rapidity, 
often becomes a predisposing cause of disease. So long as the 
various processes of secretion and excretion go on regularly, all 
is well ; but if any of these be materially deranged — if, for 
example, constipation occur — an abnormally large amount of 
highly stimulating blood will remain circulating in the body 
without adequate ways or means of removal, and will be driven 
in a full and rapid current to every part, producing inflammation 
in any organ which may be predisposed to it by natural or 
acquired causes. Should no such predisposition obstruct its 
onward flow, the vessels in some part may give way. Thus arise 
various kinds of hcemorrhar/e, and in no organ are these more 
common or more to be dreaded than in the brain, where the 
blood-vessels are large, numerous, delicate, and but feebly sup- 
ported by the soft cerebral mass in which they lie. From 
rupture or excessive distension these vessels sometimes allow of 
the pouring out of blood or of the serum of the blood, consti- 
tuting the usual form of the disease generally known as apoplexy. 
The most common symptoms of this affection are sudden loss of 
perception and power of motion, and gradually increasing coma, 
which destroys life more or less suddenly. In predisposed sub- 
jects such apoplectic attacks are often induced by sudden 
changes from poor to rich pastures, by long and fatiguing jour- 
neys during hot weather, or by any causes which give rise to 
