But when a little more time has elapsed and the nineteenth century can be properly studied from the semantic point of view, there is little reason to doubt that the interfusion of mechanical and biological conceptions and the penetration of both into meaning will present one of its most striking features. One of the greatest triumphs of mechanism—greater than the Forth Bridge or the St. Gothard Tunnel—is the fact that it has wormed itself into the meaning of the word _cause_. This is, of course, a word which tends to alter its meaning a little every time it is used, and there is evidence that in former times, while there were separate words to express such separate ideas as “bringing to birth”, “making to grow”, “being guilty of”, ... there was no general term into which the one single essence common to all these relations had been distilled. The Greek and Latin words for _cause_, for example, were both closely connected from the earliest times with their legal procedure (cf. _ac-cuse_, etc., and the modern use of _cause_ in the same sense). At some period, however—perhaps in the last two centuries before our era—such a concept must have been precipitated, and we find Cicero defining the Latin ‘causa’, with mathematical precision, simply as ‘that which effects the thing of which it is the cause’. The fascination which this abstraction exerted on the medieval imagination may be judged from the fact that the writer of a fifteenth-century treatise on Love introduced into it the sentence: “Every cause of a cause is cause of thing caused”; and we soon find the philosophers seeking through a “chain” of causes for that First Cause, which they identified with the Almighty. By the nineteenth century this thought-system of an abstract _causality_, brought about by means of abstract “laws”, lay, like an empty house, ready to be taken over by a new owner. The new owner was mechanism. “The great abstract law of mechanical causality” (mechanischen kausalität), wrote Haeckel in 1899, “now rules the entire universe, as it does the mind of man. It is the steady, immutable pole-star, whose clear light falls on our path through the dark labyrinth of the countless separate phenomena.” Under its influence even consciousness itself was, and still is, often conceived of as being _caused_ by mechanical movements taking place within the body. We also find thought described as a _function_ of the brain. This curious word had become extremely popular; and somewhere about the sixties the noun began to be used as a verb. We hear of nerves, brain, heart, ... _functioning_ or refusing to _function_, an expression in which the mechanical flavour is especially strong.