HEREDITARY DISEASES OF HORSES. 
523 
and many imperfections of the external senses, as deafness 
and blindness. These are the most common hereditary dis- 
eases incident to man ; most of them have their analogues in 
the lower animals, in which they are also hereditary. 
Amongst horses and cattle w^e find, as in the human sub- 
ject, ample illustration of the hereditary tendency of external 
form, disposition, habit, and disease. The parent transfers to 
its offspring size, shape, and general conformation similar to 
its own ; and the aphorism “like produces like” is as appli- 
cable to faulty and disproportioned as to beautiful and sym- 
metrical form, to diseased and debilitated as to healthy and 
vigorous constitution, to gentle and tractable as to fiery and 
indomitable disposition. The size, weight, general appear- 
ance, expression of countenance, fleetness, and temper of the 
horse are all hereditary. Many illustrations might be given 
of particular families being remarkable during several gene- 
rations for good or bad points, as for well or ill-formed head ; 
for high and well-developed, or for low and weak withers ; for 
fine, strong, and well-turned, or for coarse, weak, and ill- 
formed limbs. Peculiarities of colour often extend through 
many generations, and are so constant in their transmission 
as sometimes to form one of the distinctive characteristics of a 
race. Indeed, most breeds of horses hatfe a prevailing colour, 
to which there are few exceptions. The heavy horses of 
Lincolnshire, for example, are generally black; the Cleve- 
land, bay ; and the wild horses of the plains of Eastern 
Siberia, dun. Particular markings, also — as white spots on 
various parts of the body, stars and blazes on the face, one or 
more white feet or legs — often continue for many generations 
peculiar to certain families. 
The general constitution of an animal is no less hereditary 
than the external qualities to which we have just alluded. Some 
stocks of horses, for example, can sustain with impunity an 
amount of labour which, in others of the same breed, would 
cause serious bad effects ; and the peculiar action both of 
medicines, and of morbific causes, is generally observed to be 
similar in members of the same family. But besides the 
general constitution of the parents, their special condition at 
the time of copulation also appears to be to a certain extent 
transmitted to the offspring; and hence the necessity of 
selecting for breeding purposes only animals of a strong and 
healthy constitution, and of using them only when they are 
in full possession of all their physical energies. For a high 
state of the physical energies at the time of impregnation is 
believed to induce a correspondingly great development of 
physical power in the offspring ; and of this we have a curious 
