"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 having the arrangement necessary for the purposes of the turf, while the thorough-bred is as ill adapted for the dray. Animals are therefore to be selected for the individual purposes for which they are intended, with the modifications of form proper for the different uses to which they are to be applied; but for whatever purpose they may be intended, there are some points which are common to all, in the adjustment of the individual parts. If the bones want their due proportions, or are imperfectly placed--if the muscles or tendons want their proper levers--if the flexions of the joints be interrupted by the defectiveness of their mechanism, the animal must either be defective in motion or strength; the bones have irregular pressure, and if they do not break, become diseased; if the muscles or tendons do not become sprained or ruptured, they are defective in their action; if friction or inflammation does not take place in the joints, the motions are awkward and grotesque. As in every other machine, the beauty of the animate, whether in motion or at rest, depends upon the arrangement of the individual parts." CHAPTER IX. BREEDING IN THE LINE.