If in any respect such an enquiry can be made definite and therefore profitable, it is clearly in regard of Language. This, as said above, is an essential adjunct of reason such as ours, and on the other hand it forms the plainest boundary between the domain of the human race and that of the brutes. It is, says Professor Max Müller, our Rubicon on the hither side of which men alone are found. Given reason such as ours, whatever mode of communication might be open to them, we cannot suppose its possessors failing to establish a medium of intercourse. In existing conditions, man can make an alphabet out of the clicks of a needle or the flashes of a mirror, and if his vocal organs were no better than those of a baboon, we cannot imagine him content generation after generation with inarticulate howls and yells. But this is just the case of the animals. They are _never_ found to make the smallest progress in the direction of a code of signals. Dogs indeed, as Mr. Darwin says,[111] having developed in captivity the new art of barking, have further learnt to vary this accomplishment according to the circumstances that provoke it, and have distinct tones to express the diversity of their feelings, as when hunting, or angry, or setting out for a walk, or shut up in a kennel or out of a house. Some dogs, he might have added, refine still further, and will betray by their style of bark not only that they are hunting something, but what it is that they have come upon, whether a rabbit, a cat, or a hedgehog. But, as the Chevalier Bunsen observes,[112] and his observation includes such manifestations as the above: Animal sounds are the echoes of blind instincts within, or of the phenomena of the outward world, uttered by suffering or satisfied animal nature, and in all cases resulting from mere passiveness. By rational language, on the other hand, is signified, to quote Mr. Mivart:[113] The external manifestation, whether by sound or gesture, of general conceptions:--not emotional expressions or the manifestations of sensible impressions, but enunciations of distinct judgments as to "the what," "the how," and "the why." Consequently, as Bunsen declares: