This leads us to an interesting aspect of the modern jury trial.
When no other defence to homicide is possible the claim of insanity is frequently interposed.

Nothing is more confusing to the ordinary juryman than trying to determine the probative value of evidence touching unsoundness of mind, and the application thereto of the legal test of criminal responsibility.

In point of fact, juries are hardly to be blamed for this, since the law itself is antiquated and the subject one abounding in difficulty.

Unfortunately the opportunity for vague yet damaging testimony on the part of experts, the ease with which any desired opinion can be defended by a slight alteration in the hypothetical facts, and the practical impossibility of exposure, have been seized upon with avidity by a score or more of unscrupulous alienists who are prepared to sell their services to the highest bidder.
These men are all the more dangerous because, clever students of mental disease and thorough masters of their subject as they are, they are able by adroit qualifications and skilful evasions to make half-truths seem as convincing as whole ones.

They ask and receive large sums for their services, and their dishonest testimony must be met and refuted by the evidence of honest physicians, who, by virtue of their attainments, have a right to demand substantial fees.