The evidence as to these facts, which was put forward at the trial, was regarded by the jury as conclusive proof that poison had been given to the man, notwithstanding the objections pressed by the defence that the poison had not been found in his body, and that, since none of the soup was left for examination, it had not been proved that the soup was poisonous.
With the more refined methods of analysis now available, such evidence would probably have been corroborated, seeing that the tests are capable of detecting arsenic even in the minute proportion of one part in sixty millions.
In a remarkable trial that took place, in 1831, at the Warwick Assizes, expert evidence that an animal had not been poisoned supplied the proof required to establish the guilt of the prisoner. A woman named Mary Higgins was accused of having poisoned her uncle with arsenic. It was proved that he had died from an irritant poison, and there was also abundant proof that the niece had bought arsenic. Her explanation of this was that she had wanted it to destroy vermin, and by way of adding conviction to her story she actually produced a dead mouse, which, she alleged, had been killed by the poison. This proved a fatal blunder on her part, for an examination of the mouse showed that there was no arsenic whatever in its body. The defence was therefore discredited, and the prisoner was found guilty of murder.
The most valuable applications of physiological tests have been in cases where narcotic poisons have been used, and especially in the early days of chemical analyses, when the methods then known were incapable of identifying these poisons.
For example, in the year 1838 a woman was tried at Liverpool on a charge of having sent a poisoned pudding to another woman with the intention of poisoning her. The two children who were sent with the pudding tasted it on the way, and finding that it was bitter, mentioned the fact to the woman to whom they were taking it. She had other reasons for being suspicious, and, therefore, sent the pudding to a doctor to be examined. He applied various tests, but was unable to detect the presence of any poison, although from the taste he suspected that some narcotic poison was present.