These periods may be called that of growth, the stationary period, and that of decline. The veterinarian is the expert referee in all questions of age, and any addition to our knowledge in regard to it needs no apology. If animals lived a perfectly equable life, the changes which take place in their form and character would be regular and easy to appreciate; but, from overwork, from the alterations produced by excessive food, want of food, or irritant substances; from the effects of variable surroundings, at times trying on the constitution, at other times rendering the external tissues deli cate and sensitive to exposure, the wear and tear on them is irregular. Excessive work in one animal and want of food in another open easy avenues for the ravages of time, which would not show on one which was better nourished and better cared for. The well-bred colt training over fast miles from a yearling. And the great draught-horse hauling a load of several tons in our large cities, demand excess of food for their herculean tasks. The greater quantity of food overtaxes the organs in proportion, and, in the same number of years, one animal may live double that of another in usefulness and functional activity.