We may now turn to a consideration of the subject-matter and the main ideas of Browning's poetry. From whatever point of view we regard his work, we find that ultimately the emphasis rests on the same great central fact, the supremacy of his interest in human nature. This dominating interest is shown, for instance, by a study of his treatment of physical nature. To be sure, no one can read his poems without recognizing the truth that his use of natural facts is distinctive in kind and very stimulating. A mere reference to the pictures of the sky in _Pippa Passes_, the vivid descriptions of fruits and flowers in "An Englishman in Italy," the remarkable studies of small animal life in "Saul" and "Caliban upon Setebos," of birds in "Home-Thoughts, from Abroad," of insects in the first part of _Paracelsus_ and in many later poems, suffices to show that in mature life he did not lose the keenness of observation and interest characteristic of his youth. Yet it is also evident that his use of nature by way of direct description, or even as illustrative material, is far less in amount than that of other notable nineteenth century poets. He cares much less for "the river's line, the mountains round it and the sky above" than for the "figures of man, woman, and child these are frame to." Where nature is drawn upon, it is almost invariably in complete subordination to some human interest, and its literary form is almost always that of casual mention, background, or similitude, and the first of these is the most frequent. Furthermore, nearly all these passages are a mere statement of observed fact without comment or interpretation. There is one great passage in _Paracelsus_ where the joy of God in the act of creation is depicted; there are occasional references to the delight of man in the external world; and now and then, as in "By the Fireside," man and nature are intimately fused; but such conceptions rarely occur. In Browning's poetry the boundary lines between man and nature are clearly marked. In _Paracelsus_ he definitely protests against man's way of reading his own moods into nature, and of attributing to her his own qualities and emotions. He also always accounts man, if he has truly entered into his spiritual heritage, as consciously superior to nature. The troubadour Eglamour, in _Sordello_, says that man shrinks to naught if matched with a quiet sea or sky, but Browning calls that Eglamour's "false thought." To Browning, nature was to be studied, enjoyed, and used, but it was not as to Keats a realm of enchantment; or as to Wordsworth the realm where alone the divine and the human could pass the boundaries of sense and meet; or as to Matthew Arnold a refuge from pain and disillusionment. Browning regards the world about him more in the sane, unsentimental, straightforward, intelligible way of Chaucer or of Shakespeare. The mystical elements in Wordsworth's feeling for nature were foreign to Browning's mind.