_The Work of Claude Bernard. Exclusion of Vital Force, of Vital Cause, of the “Caprice” of Living Nature._—It is not, however, a slight advance or inconsiderable advantage to have eliminated vitalistic hypotheses from almost the whole domain of present-day physiology, and to have them, as it were, thrown back into its hinterland. This is the work of the scientific men of the first half of the nineteenth century, and particularly of Claude Bernard, who has thereby won the name of the founder or lawgiver of physiology. They found in the old medical school an obstinate adversary glorying in its sterile traditions. In vain was it proved that vital force cannot be an efficient cause; that it was a creation of the brain, an insubstantial phantom introduced into the anatomical marionette and moving it by strings at the will of any one—its adepts having only to confer upon it a new kind of activity to account for the new act. All that had been shown with the utmost clearness by Bonnet of Geneva, and by many others. It had also been said that the teleological explanation is equally futile, since it assigns to the present, which exists, an inaccessible, and evidently ultimately inadequate cause, which does not yet exist. These objections were in vain. _Determinism._—And so it was not by theoretical arguments that the celebrated physiologist dealt with his adversaries, but by a kind of lesson on things. In fact he was continually showing by examples that vitalism and the theory of final causes were idle errors which led astray experimental investigation; that they had prevented the progress of research and the discovery of the truth in every case and on every point in which they had been invoked. He laid down the principle of _biological determinism_, which is nothing but the negation of the “caprice” of living nature. This postulate, so evident that there was no need to enunciate it in the physical sciences, had to be shouted from the housetops for the benefit of supporters of vital spontaneity. It is the statement that, under determined circumstances materially identical, the same vital phenomena will be identically reproduced.