656 
EDITORIAL OBSERVATIONS. 
add, its relation to other vicinous or correlative structures ; 
“ the ground of our reasoning resting chiefly on the analogy 
which subsists in all respects between external and internal 
parts. Our conclusion is, therefore, that every hereditary dis- 
ease depends upon some hereditary abnormal condition predisposing 
to that disease,” on the principle that “ like produces like.” 
Proceeding to the consideration of “ The hereditary diseases 
of horses,” as divided from those of cattle, Mr. Dun enume- 
rates, first, those of a “ local nature,” bone-spavin, curb, 
navicularthritis ; and, secondly, u those which are more gene- 
ral in their character, and which affect the system as a whole,” 
viz., chronic cough, roaring, ophthalmia periodica, and blind- 
ness. 
In regard to local hereditary diseases, Mr. Dun makes the 
observation that they are “ usually simple in their nature, 
and consequently their predisposing causes are easily traced, 
and usually consist in some peculiarity of external form more 
or less obvious. This observation chiefly applies to several 
sorts of lameness,” &c. Thus, with the principle on which 
he set out, he traces hereditary bone-spavin to the “ width 
and strength of the limb below the hock being disproportioned 
to its width and strength above it.” Admitting that bony 
deposits are more apt to affect some families than others — in 
fine, such a thing as an osseous or bone-forming diathesis 
seeming to be implanted in the system by Nature with the 
intention of strengthening “ local weaknesses,” and mani- 
fested from very slight causes ; w r e say, with this notion of 
local hereditary disease, Mr. Dun observes, in respect to the 
disease deranging the constitution, that “it cannot be doubted 
that there exists in them (it) some peculiarity of conforma- 
tion or of minute texture differing from health, and which, 
although generally unobservable, is yet capable, under 
favouring circumstances, of fostering serious and irremediable 
disease.” We may, at another time, resume the considera- 
tion of this interesting subject. 
