ON THE CAUSE’ OF DISEASE. 21 
affected, or of some disturbance of the relation which should subsist 
between the different constituents of these parts. This abnormal 
state of the internal parts is seldom within the limits of our means 
of observation or investigation ; but its existing in animals having 
an hereditary predisposition to disease can not, we think, be doubted, 
as we shall now endeavor to show. The ground of our reasoning 
rests chiefly on the analogy which subsists, in all respects, between 
external and internal parts. The same law which regulates the 
hereditary transmission of form, texture, and relation of external 
and visible parts, also operates with equal force in regard to the 
form, texture, and relations betwixt the component parts of inter- 
nal, and, it may be, inaccessible to ordinary powers of investiga- 
tion. Then if, as we have shown, external hereditary diseases, 
such as lamenesses, are traceable to external hereditary peculiari- 
ties of conformation, we do not think it pushing our analogy too 
far in asserting that, in like manner, internal hereditary diseases 
must, in great part at least, depend upon some inherent hereditary 
veculiarity of the internal parts affected.” 
The common disease known as bone spavin is inherent, or de- 
pendent on predisposition, as related above; for the author never 
knew a horse to be the subject of this malady unless he had faulty 
hocks; or, in other words, in so far as the conformation of the 
parts were concerned, predisposition was evident. The same re 
marks apply to ringbone. LHither the pasterns are too upright, 
thereby causing jar and concussion, or they slant unnaturally, 
aud the consequence is, strain of the ligamentary structures, end- 
ing often in ringbone and other osseous diseases. 
Ample evidence can be adduced to show that various diseases 
of the eye are hereditary. The tendency to ophthalmia shows it- 
self in a peculiar conformation of the eye, and parts in the vicinity 
of it. Periodical ophthalmia is notoriously hereditary, and usually 
ends in cataract. 
Colic, also, can be traced to inherent tendencies; for animals 
subject to flatulent colic are known to have a morbid appetite; 
they have, also, a large, roomy abdomen, which gives them an 
ungainly appearance. Yet it is true that diseases may occur 
accidentally, without the intervention of predisposition ; but pre- 
disposition exists in almost all cases, and it only requires some 
anatomical and physiological knowledge on the part of husband- 
men to detect it. 
