They tell us distinctly that the knife is Ellis's knife and I don't see any answer to that."
"There is no answer because there has been no statement. The bloodhounds have told you nothing. You have drawn certain inferences from their actions, but those inferences may be totally wrong and they are certainly not evidence."
"You don't seem to have much opinion of bloodhounds," the inspector remarked.
"As agents for the detection of crime," replied Thorndyke, "I regard them as useless. You cannot put a bloodhound in the witness-box. You can get no intelligible statement from it. If it possesses any knowledge, it has no means of communicating it. The fact is," he continued, "that the entire system of using bloodhounds for criminal detection is based on a fallacy. In the American plantations these animals were used with great success for tracking runaway slaves. But the slave was a known individual. All that was required was to ascertain his whereabouts. That is not the problem that is presented in the detection of a crime. The detective is not concerned in establishing the whereabouts of a known individual, but in discovering the identity of an unknown individual. And for this purpose bloodhounds are useless. They may discover such identity, but they cannot communicate their knowledge. If the criminal is unknown, they cannot
