160 HEREDITARY DISEASES OF HORSES AND CATTLE. 
contraction, the latter when a manifest alteration in the form 
of the foot precedes the lameness. Hence, breeders should 
at all times look with very considerable suspicion on a stal- 
lion exhibiting narrow, contracted, upright hoofs; for although 
we may occasionally observe old horses, having contracted 
feet and otherwise out of shape, performing their work with- 
out lameness, yet such horses should be invariably avoided 
in breeding. 
Mr. Thomas Turner, Y.S., Croydon, related an interesting 
case respecting the hereditary nature of the navicular disease, 
at a meeting of the Veterinary Medical Association,* well 
worth mentioning here — that of a colt bred by himself, which 
became lame from this disease at four years old. Both the 
sire and dam of the colt had narrow, contracted feet; and the 
mare, becoming unfitted for work, was destroyed. On dis- 
secting the foot which exhibited the greatest amount of 
disease, he discovered a hole in the navicular bone; and, 
strange as it may appear, the colt’s lameness existed in the 
corresponding foot ; and, what appears still more curious, 
the dam had a rat-tail, and the colt had a facsimile of it. 
In the examples given we have positive evidence of diseased 
action arising from peculiarity of structure, and transmissible 
by descent. The breeder may learn a useful lesson from 
them — that, in selecting horses to breed from, it is not enough 
to direct his attention to pedigree chiefly, but he should be also 
guided in his judgment by external conformation. The ani- 
mal machine may be put in motion by the noblest blood, but 
unless every bone has its just proportion, every muscle its 
proper pulley, and every lever its due length and arrange- 
ment, the motion can never be accurate, vigorous, and durable. 
We will next direct our attention to some important diseases 
of the internal parts of the body , depending on something defective 
or ill-balanced in the organization . On the first view it might 
appear that such deviations were less extensive than those of 
outward conformation ; but there is reason to believe that 
they occur far more frequently than is generally imagined. 
Dr. Holland says, “ that there is scarcely any organ of im- 
portance which does not afford evidence of diseased actions 
derived from structure, and transmissible by descent. On 
looking to the textures more widely diffused through the 
body — as the different vascular systems, the nerves, &c. — 
we have every reason to suppose, though the proof be less 
direct, that they are subject to hereditary variations of struc- 
ture, not merely in detached parts of each system, but 
throughout those minute branches and terminations where 
* See Trans., January 20, 1839. 
