I have frequently interlaced my fingers with those of some person whom they dislike, and extending the hand towards them, they rarely make a mistake by getting hold of the wrong finger, and yet it has frequently occurred that they could not see the hands at all, and had to depend alone upon the sense of touch. In cases where the hands were very nearly the same size they were not able to select the fingers so readily, but where a lady's hand was used, or that of a boy, the selection was made without hesitancy and without error. I have tried this experiment a great many times with a view to ascertaining to some extent the delicacy of their sense of touch. Another fact that I may mention is, that they do not habitually smell articles of food or other things given to them; but they depend chiefly upon their sight for finding and their taste for choosing their food. My opinion is, that the sense of smell does not play an important part in these affairs. I may add, too, that, in the Cebus, his tail is perhaps the most sensitive organ of touch, although it is not used in this capacity to any great extent. He is generally very watchful over this useful member, because it serves him in so many ways, and I think perhaps it is safe to say that the tail is the last part of the monkey that ever becomes tame. CHAPTER XIII. The Extent of my Experiments--Apes and Baboons--Miscellaneous Records of Sound--The Vocal Index. In quest of the great secret of speech, I have pursued my investigations chiefly in the direction of learning one tongue, but incidentally I have made many detours, and I have recorded the sounds of many other forms of the animal kingdom, besides primates. I have examined the phonation of lions, tigers, leopards, cats, dogs, birds of many kinds, and the human voice in speech, music, and laughter. Besides these, I have examined various musical sounds, especially of the pipe and whistle kinds.