644 FRAGMENTS OF SCIENCE. 
pared for its introduction, then, I think, lie is right, and 
that, as a matter of social policy, Dr. Haeckel would be 
wrong in seeking to antedate the period of its introduction. 
In dealing with the community great changes must have 
timeliness as well as truth upon their side. But if the 
mouths of thinkers be stopped, the necessary social prepa- 
ration will be impossible; an unwholesome divorce will be 
established between the expert and the public, and the 
slow and natural process of leavening the social lump by 
discovery and discussion will be displaced by something 
far less safe and salutary. 
The burden, however, of this celebrated lecture is a 
warning that a marked distinction ought to be made be- 
tween that which is experimentally proved, 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 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 con- 
siders, 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 
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 connec- 
tion 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 re- 
search are expressed as problems (or hypotheses). We 
