After a trial lasting twelve days, the judge (Lord Campbell) summed up the evidence, and dwelt in strong terms upon the scientific witnesses for the defence (see _ante_, p. 19). With reference to the fact that no strychnine had been detected in the body, he remarked that "there was no rule of law according to which the poison must be found in the body of the deceased, and all they knew respecting the poison not being found in the body was that in that part of the body that was analysed by the witnesses no strychnia had been found." Since physiological tests are, in many cases, much more sensitive than chemical tests, they have often been used for the identification of traces of poison isolated from a body. Thus a small quantity of a particular alkaloid will produce certain characteristic physiological results when injected into the circulatory system of a small animal, and should precisely the same results be obtained by the injection of the unknown substance, the obvious inference to be drawn is that the two substances are identical. At the same time it has been shown on more than one occasion that it is not justifiable to draw a comparison between the quantitative action of a particular poison upon an animal and upon man. As an instance of the danger of relying too exclusively upon the results of experiments upon an animal, the interesting case of Freeman, who was tried at Leicester in 1829, may be mentioned. A young woman, the servant of a chemist in the town, was found dead in bed. She had evidently died from the effects of prussic acid, and from the fact that the one ounce bottle from which the poison had been taken still contained three and a half drachms, it was inferred that she had taken four and a half drachms. Owing to the facts that the arms of the dead woman were crossed upon her breast, and that the clothes had been pulled up neatly over them, while the bottle containing the remainder of the poison had been re-corked and was lying by her side, it was thought that it was not a case of suicide, but that the poison must have been given to her. Suspicion fell upon a young man named Freeman, who was an assistant of the chemist, and he was charged with having murdered the woman. The point urged by the prosecution was that the action of prussic acid was so rapid, that it was impossible for the woman to have had the time to take the amount which had apparently been taken, and subsequently to have arranged the bed-clothes and corked the bottle. Expert evidence upon this question was given by five doctors, four of whom gave as their opinion that these things could not have been done by the woman herself. In support of their view, one of them stated that the same quantity of prussic acid had killed a dog in three seconds. Fortunately for the prisoner he was able to produce conclusive evidence of his innocence, and the jury, therefore, very rightly refused to accept the medical opinion.