In the process of training, the presence of the tame ones can generally be dispensed with after two months, and the captive may then be ridden by the driver alone; and after three or four months he may, so far as regards docility, be entrusted with labour; but it is undesirable, and even involves the risk of its life, to work an elephant too soon; it has frequently happened that a valuable animal has laid down and died the first time it was tried in harness, from what the natives believe to be “broken heart,”—certainly without any cause inferable from injury or previous disease.[148] It is observable, that till a captured elephant begins to relish food, and grow fat upon it, he becomes so fretted by work, that it kills him in an incredibly short space of time. The first employment to which an elephant is put is to tread clay in a brick-field, or to draw a waggon in double harness with a tame companion. But the work in which the display of sagacity renders his labour of the highest value, is that which involves the moving of heavy materials; and hence in dragging and piling timber, or conveying stones[149] for the construction of retaining walls and the approaches to bridges his services in an unopened country are of the utmost importance. When roads are to be constructed along the face of steep declivities, and the space is so contracted that risk is incurred either of the working elephant falling over the precipice or of rocks slipping down from above, not only are the measures to which he resorts the most judicious and reasonable that could be devised, but if urged by his keeper to adopt any other, he manifests a reluctance sufficient to show that he has balanced in his own mind the comparative advantages of each. An elephant appears on all occasions to comprehend the purpose and object that he is expected to promote, and hence he voluntarily executes a variety of details without any guidance whatever from his keeper. This is one characteristic in which this animal manifests a superiority over the horse; although an elephant’s strength in proportion to its weight is not so great as that of the latter.