Page:Popular Science Monthly Volume 17.djvu/376

362, by what we might call locomotive memory—i. e., the faculty to remember a long series of turns in their due sequence and with the correct intervals of time or space. The sense of touch becomes here vicarious to eyesight. In the same way a wide-awake animal might take cognizance of certain locomotive data without the assistance of its eyes. It might feel the turnings of its rolling cage, and remember enough to imply the general direction. A stupefied animal could not do it. The olfactory power of a dog exceeds ours about as much as human eyesight exceeds that of a shrew-mouse. A dog will "set" a covey of partridges across a broad field, and can scent a tramp from a distance of half a mile. A nose that can track the faint scent of a rabbit through thickets of aromatic herbage might easily distinguish the atmosphere of a reeking manufacturing town at a distance of ten miles. At fifty miles it might be barely possible under the most favorable conditions of wind and weather; at one hundred and fifty miles it seems impossible under all circumstances. Besides, a dog would find his way to a backwoods cabin as readily as to a smoky metropolis. The question still recurs: How does he manage it? Should dogs be gifted with the faculty of determining geographical latitude and longitude by means of their noses?

The memory-hypothesis being disposed of, the scent-theory might be definitely settled by a simple operation, viz., destruction of the olfactory nerve. Any anatomist could do it. Helmholtz and Von Graefe made similar experiments with the optic nerve, even without inflicting permanent damage. A dog might be rendered scentless for a day or two, and a trip to the next county under the above-described collateral precautions would decide the point. Deerhounds, pointers, and terriers would be the best subjects. for the experiment; greyhounds are not only inferior in acuteness of scent but in sagacity in general; and collies and poodles, though marvelously clever in their peculiar spheres, seem to be almost destitute of what the French call the sens d'orientation (the sense of orientation—the process of determining the points of the compass).

Leaving the exegetical question out of view, I will here venture a conjecture in regard to the origin, or rather the original purpose, of the strange faculty. The common ancestor of all domestic dogs was probably some near relative of the Canis lupus, either the dog-wolf of the Hindoo-Koosh, or the Canis aureus, the Indian or African jackal. The puppies of all these canines are born in litters—from six to ten at a time, are helpless for the first ten weeks, and entail a great amount of trouble on their food-purveyors. The mother, perhaps straitened in her own means of support, has now to meet the demands of a greatly enlarged household, and in all probability the available supplies of animal food in her next neighborhood will soon be exhausted. Her forage excursions must be extended to greater and greater distances, in a barren country like northern Africa or