So long as the term "blood" is used to convey the idea of definite hereditary qualities it may not be objectionable. We frequently use expressions which are not strictly accurate, as when we speak of the sun's rising and setting, and so long as every body knows that we refer to apparent position and not to any motion of the sun, no false ideas are conveyed. But to suppose that the hereditary qualities of an animal attach to the blood more than to any other fluid or to any of the tissues of the body, or that the blood of a high-bred horse is essentially different from that of another, is entirely erroneous. The qualities of an animal depend upon its organization and endowments, and the blood is only the vehicle by which these are nourished and sustained;--moreover the blood varies in quality, composition and amount, according to the food eaten, the air breathed and the exercise taken. If one horse is better than another it is not because the fluid in his veins is of superior quality, but rather because his structure is more perfect mechanically, and because nervous energy is present in fitting amount and intensity. For illustration, 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.