155 
Extracts from British and Foreign Journals. 
ON THE HEREDITARY DISEASES OE HORSES AND CATTLE. 
By W. F. Karkeek, M.R.C.V.S., Truro. 
{A Prize Essay.) 
Although certain determinate characters and forms, perpe- 
tuated by generation, distinguish the several races or breeds 
of horses and cattle in this and other countries, yet these 
distinctive marks are not so arbitrarily fixed, but that indi- 
viduals, in any one of those breeds, may and do differ among 
themselves, in constitution and temperament, as they are 
severally affected by varieties of organization, disposing them 
to different diseases. These predispositions, no less than the 
varieties of size, form, colour, and other obvious properties, 
are hereditary and transmissible to offspring; and though 
the direct proof may not be equal for the two cases, and the 
effects resulting are of such different importance, yet is it 
certain that the peculiarities so carried on, from one genera- 
tion to another, have reference to one common law. 
Without entering minutely into the consideration of the 
cause of such deviations from the primitive or common type 
of the species, we may remark that certain external circum- 
stances, as food, climate, and domesticity, appear to have had 
considerable power in modifying animal organization. Pos- 
sibly the most important influence in this respect is due to 
the artificial mode of life which some animals lead under 
the control of man, by which modifications are induced to a 
certain extent and are transmissible to offspring. It is to 
this influence that we may probably attribute the occasional 
production of accidental varieties — many instances of which 
may be cited as examples of this singular phenomenon in 
the reproduction of the species. Thus the polled breeds of 
cattle sprang from an individual variety, which was preserved 
by the Scotch farmers, on the supposition that such formed 
animals would become more quiet and less apt to gore one 
another than the native races 
The 4 Ancon’ or ‘ Otter’ breed of sheep, now established 
in America, is another striking instance of departure from a 
common type — a variety that was preserved in consequence 
of their short otter-like limbs, which prevented them from 
leaping fences. We have also another singular example in 
those races of dogs that have a supernumerary toe on the 
