The yellow fog that rubs its back upon the window-panes, / The yellow smoke that rubs its muzzle on the window-panes,

the ciliated epithelium of the windpipe

This recalls the Victorian embarrassment with utility, the decorative euphemism which sheathed chairs in antimacassars, pudically curtained table legs, and named railway engines after chivalric warriors; but there's more to it than that.

[T]here are beings [who] . . . revel, with a lively zest, among all the things that are most foul and loathsome. . . . Sensuality, force of temper, inertness, obtundity of perception, personal idolatry, and the destitution of the higher and better emotions of humanity, are the ingredients of a constitution of this order.