Science has made no real progress towards solving the enigma of vitality. Its evasiveness becomes, on the contrary, more apparent as inquiry is rendered more exact. Under a laxer discipline of thought the contrast between life and death seemed less glaring. It was easily taken for granted that creeping things were engendered by corruption, aid being invoked, if required, from the _virtus cœlestis_ of the eighth sphere. Thus, the birth of mice from the damp earth was, in the ninth century, held to be signified by the word _mus_ (=humus);[119] and Van Helmont, at the height of the revival of learning, published without misgiving a recipe for the creation of the same animals.[120] Yet there was already better knowledge to be had for the asking; and Francesco Redi, in 1668, crystallized Harvey's opinion in the celebrated maxim, '_Omne vivum ex vivo._' Its truth is incontrovertible. Challenged and tested again and again, it has as often been vindicated, and may now be said, despite certain anomalous effects of radium on veal broth, to stand outside the legitimate range of debate. 'That life is an antecedent to life,' Lord Kelvin declared in 1871, 'seems to me as sure a teaching of science as the law of gravitation.'[121] But the succession is not easy to start within the terms of a strictly uniformitarian convention. The expedient is tempting, if scarcely satisfactory, of demanding from the past what we dare not claim from the present. Two and a half millenniums ago it was already in vogue. Herodotus dismisses a genealogical embarrassment with the remark, γένοιτο δ'άν πᾶν έν τῶ μακρῶ χρόνω, which may be freely translated, 'In the long run of time anything may happen.' Conditions, we are apt to think, may have been more elastic long ago. The proven impossibility of to-day becomes vaguely thinkable seen through the mist of uncounted yesterdays. 'If it were given to me,' Professor Huxley said,[122] 'to look beyond the abyss of geologically recorded time to the still more remote period when the earth was passing through physical and chemical conditions which it can no more see again than a man can recall his infancy, I should expect to be a witness of the evolution of living protoplasm from non-living matter.' To these first vital compounds he attributed a fungoid nature and mode of growth, and the choice deprived his speculation of any plausibility that might otherwise have belonged to it. Fungi are not self-supporting; they cannot supply themselves with nourishment from the raw materials of the mineral world; they depend upon the hospitality of differently organized beings. They were, then, certainly not among the 'first mercies of nature.' Mr. Herbert Spencer, too, was inclined to regard spontaneous generation as a superannuated process. The leap from the non-vital to the vital, now admitted by the saner kind of biologists to be impracticable, might have been taken, it seemed to him, when 'the heat of the earth's