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the starting-point in the inductive method which he followed, he saw clearly that it was valueless until he had put it to the proof by questioning Nature. Few among that vociferating crowd of anti-vivisectionists know that he did not shrink from observing for himself what was going on in the circulation of living animals. If he had not done so, he could not have obtained the sure answer to his questions—the proof of his hypothesis. The answer was in his case definite and unmistakeable. There was no longer any possibility of denying the truth of the facts, or disputing the conclusions deduced from them. It is much to be regretted that some philosophers of the present day, some close observers, have been content with a line of argument falling short of that certainty which, in my opinion, is at all times true of what I have already classed as laws of Nature. When the questioning of Nature has not produced an answer in accordance with their expectation, it has been not unusual to substitute a pretty and perhaps plausible theory as the main prop of the hypothesis, in place of abandoning it as a delusion which could only lead away from the strict path of scientific truth.
The survival of the fittest is by no means a new idea among physiologists. It was recognised, in its relation to the many varieties of the races of man, by Pritchard, when he wrote on this subject
