HEREDITY OF DISEASES. 35 



viduals of the same stock, and their long continuance, 

 even under the best management and most efficient 

 systems of breeding. Such characters indicate pro- 

 clivity to certain diseases, as swelled legs, weed, and 

 grease." 1 



If the leg below the hock is disproportionately 

 long, and the os calcis is short (giving a narrow hock), 

 a strain of the joint, or some other form of disease, is 

 liable to result from an amount of work that would 

 not be severe in a limb of proper proportions. 



Any marked dilatation or contraction of the blood- 

 vessels gives a tendency to irregularities of the circu- 

 lation when the work performed is severe, and a con- 

 sequent predisposition to congestion or inflammation 

 of important organs. 



Like an engine with a fly-wheel that is not per- 

 fectly balanced, the animal organization of faulty pro- 

 portions is enabled to perform a moderate amount of 

 work without difficulty ; but, when the machinery is 

 taxed nearly to its full capacity, the defective adjust- 

 ment becomes a source of danger, involving the in- 

 tegrity of other parts of the system. 



This indirect transmission of a predisposition to 

 disease, through a faulty proportion of parts, is of 

 frequent occurrence, and it will undoubtedly explain 

 many of the cases of disease appearing suddenly, 

 without apparent cause, and in which an heredi- 

 tary taint was not suspected, from the fact that the 

 ancestors were not affected with the disease in any 

 form. 



This form of hereditary transmission furnishes a 



1 Journal of the Royal Agricultural Society^ vol. xiv., p. 121. 



