take two horses--one so built and endowed that he
can draw two tons or more, three miles in an hour; the other so that
he can trot a mile in three minutes or less. Let us suppose the blood
coursing in the veins of each to be transferred to the other; would
the draft horse acquire speed thereby, or the trotter acquire power?
Just as much and no more as if you fed each for a month with the hay,
oats and water intended for the other.

It is well to attend to pedigree, for thus only can we know what are
the hereditary qualities, but it is not well to lay too much stress
upon "blood," What matters it that my horse was sired by such a one or
such a one, if he be himself defective? In breeding horses,
_structure_ is first, and endowment with nervous energy is next to be
seen to, and then pedigree--afterwards that these be fittingly united,
by proper selection for coupling, in order to secure the highest
degree of probability which the nature of the case admits, that the
offspring may prove a perfect machine and be suitably endowed with
motive power.

"The body of an animal is a piece of mechanism, the moving power of
which is the vital principle, which like fire to the steam engine sets
the whole in motion; but whatever quantity of fire or vital energy may
be applied, neither the animal machine nor the engine will work with
regularity and effect, unless the individual parts of which the
machine is composed are properly adjusted and fitted for the purposes
for which they are intended; or if it is found that the machine does
move by the increase of moving power, still the motion is irregular
and imperfect; the bolts and joints are continually giving way, there
is a continued straining of the various parts, and the machine becomes
worn out and useless in half the time it might have lasted if the
proportions had been just and accurate. Such is the case with the
animal machine. It is not enough that it is put in motion by the
noblest spirit or that it is nourished by the highest blood; every
bone must have its just proportion; every muscle or tendon its proper
pulley; every lever its proper length and fulcrum; every joint its
most accurate adjustment and proper lubrication; all must have their
relative proportions and strength, before the motions of the machine
can be accurate, vigorous and durable. In every machine modifications
are required according as the purposes vary to which it is applied.
The heavy dray horse is far from