524 
HEREDITARY DISEASES Of HORSES. 
example in the fact, that the Arabs, before bringing the 
parents together, give them a short gallop, believing that the 
spirit and fleetness of the progeny is thereby enhanced. On 
the other hand, we find that even a slight and temporary de- 
bility at the time of copulation exercises a marked deteri- 
orating effect upon the spirit and vigour of the offspring, and 
it is well known that the stock of old stallions is generally 
weak and spiritless : “Senes valetudinarii, imbecilles . . . filios 
vitios constitutione gignunt. 55 — Fernel . 
It must be observed that external circumstances, as diet 
and temperature, exercise a powerful influence on animal 
growth and development. With meager fare and exposure 
to cold, animals do not reach the average size of their race, 
and beget stock as much below average as themselves. In 
similarly unfavorable circumstances, these again do not 
reach the size even of their own immediate parents, and pro- 
create a still smaller progeny. Conditions favorable to growth 
and improvement operate in a similar manner. They improve 
each individual, and the descendants of each inherit to a 
greater or less degree the improvements on the parent stock. 
Animals, then, are altered by circumstances, and transmit to 
their progeny their altered forms. Thus, after a few genera- 
tions, the external characters of a breed are often greatly 
modified, and hence have arisen the permanent varieties of 
horses and cattle met with in different parts of the kingdom 
— the tall heavy horse of the Lincolnshire fens, the light, 
active, but powerful thorough-bred, the small pony of Shet- 
land — and amongst cattle, the short-horned, the Ayrshire, 
and West Highland breeds, and many others — varieties which 
have a common origin, but which are now so distinct and per- 
manent that each produces a progeny with its own distinctive 
characteristics. Thus, even acquired and artificial habits may 
become hereditary. Certain districts are famous for their 
trotting horses, and many Irish hunters are remarkable for 
their peculiar style of leaping. Some years ago the Earls of 
Morton and Zetland imported from Dongolia, in Upper 
Egypt, several entire horses, which were remarkable for their 
high and prancing action. Their progeny, both out of 
thorough-bred mares and those of the heavier breeds, inherited 
the action of the sires, to such a degree that they had all to 
be sold as carriage-horses, being unfit for racing, hunting, or 
almost any other kind of work. Prichard states, in his 
6 Natural History of Man, 5 * that the horses bred on the 
table-lands of the Cordilleras “are carefully taught a peculiar 
pace, which is a sort of running amble ; 55 after a few genera- 
* Second Edition, p. 35. 
