The elements of error in experimenting with inanimate objects were indicated, in a general way, by Bacon, under the strange headings "Idols of the Tribe," "Of the Den," "Of the Forum," "Of the Theatre"; and later writers on evidence and the principles of science have repeated or assumed the Baconian formulas; but the special elements of error in experimenting with living human beings have escaped conscious and exhaustive analysis. To have formulated these elements of error much sooner than the present time would have been quite impossible, for our knowledge of the involuntary life—one of the most important factors—was far too limited.
The science and art of experimenting with living human beings is indeed now in precisely the same state as the general philosophy of induction prior to the time of Bacon. Before the era of the Baconian philosophy, indeed in all eras, men had instinctively employed the inductive method, but the principles of that method had never been formulated; consequently, when philosophers reasoned or attempted to reason on the subject, they almost always went wrong. The philosophy of Bacon applies only to inanimate nature; of the art of seeking truth through experiments on living human beings—of the six sources of error in all such experiments and the means of guarding against them—he knew nothing, and evidently suspected nothing; and that branch of philosophy—of such vast import in biological investigations—has remained to this day unstudied and almost unthought of; hence, although some experimenters are saved through their instincts, others—and those the very ablest scientific geniuses of the age—never attempt to reason on the subject without falling into serious error.
In experimenting with living human beings there are, as above stated, just six sources of error, all of which are to be recognized and systematically and, if possible, also simultaneously guarded against if our results are to command the confidence and homage of science. To be guilty of overlooking, in any research, even one of these six possibilities of error, is to be guilty of overlooking all, and practically to vitiate all the results of our labors.
These six sources of error are as follows:
First Source of Error: The phenomena of the involuntary life in both the experimenter and the subject experimented on.—Under this head are embraced trance, with all its manifold symptoms, and all the interactions of mind and body that are below the plane of volition or of consciousness or of both. Without a knowledge of this side of physiology, scientific experimenting with living human beings is impossible. It is a want of this knowledge that makes most of the experiments of scientific men in this department during the past century so unsatisfactory and so ludicrous.
Second Source of Error: Unconscious deception on the part of the subject experimented on.—This unconscious deception comes
