scientific thought," but of "common modesty" and "common sense." And, though I am indebted to Prof. Clifford for recalling in the Nineteenth Century for April the public mind in this connection from heated fancy to sober fact, I do not think a brief additional examination of Virchow's views, and of my relation to them, will be out of place here.
The key-note of his position is struck in the preface to the excellent English translation of his lecture—a preface written expressly by himself. Nothing, he says, was further from his intention than any wish to disparage the great services rendered by Mr. Darwin to the advancement of biological science, of which no one has expressed more admiration than himself. On the other hand, it seemed high time to him to enter an energetic protest against the attempts that are made to proclaim the problems of research as actual facts, and the opinions of scientists as established science. On the ground, among others, that it promotes the pernicious delusions of the socialists, Virchow considers the theory of evolution dangerous; but his fidelity to truth is so great that he would brave the danger and teach the theory, if it were only proved. The burden indeed of this celebrated lecture is a warning that a marked distinction ought to be made between that which is experimentally established, and that which is still in the region of speculation. As to the latter, Virchow by no means imposes silence. He is far too sagacious a man to commit himself, at the present time of day, to any such absurdity. But he insists that it ought not to be put on the same evidential level as the former. "It ought," as he poetically expresses it "to be written in small letters under the text." The audience ought to be warned that the speculative matter is only possible, not actual truth—that it belongs to the region of "belief," and not to that of demonstration. As long as a problem continues in this speculative stage it would be mischievous, he considers, to teach it in our schools. "We ought not," he urges, "to represent our conjecture as a certainty, nor our hypothesis as a doctrine: this is inadmissible." With regard to the connection between physical processes and mental phenomena he says: "I will, indeed, willingly grant that we can find certain gradations, certain definite points at which we trace a passage from mental processes to processes purely physical, or of a physical character. Throughout this discourse I am not asserting that it will never be possible to bring psychical processes into an immediate connection with those that are physical. All I say is, that we have at present no right to set up this possible connection as a doctrine of science." In the next paragraph he reiterates his position with reference to the introduction of such topics into school-teaching. "We must draw," he says, "a strict distinction between what we wish to teach and what we wish to search for. The objects of our research are expressed as problems (or hypotheses). We need not keep them to ourselves; we are ready to communicate them to all the world, and say, 'There is the problem; that is what we strive for.'. . . The investigation of such problems,
