Is it necessary that the poison should be found in the body or in the evacuations to lead to a conviction for poisoning? On this point, Christison was of opinion that if the symptoms, _post-mortem_, appearances, and moral evidence are very strong, it is not necessary that the poison be found in order to establish a charge of poisoning. This opinion was also supported by the late Dr. Geoghehan, Professor of Medical Jurisprudence in the Royal College of Surgeons, Ireland, and was also virtually acted upon in the case of Palmer, where the non-detection of strychnia was strongly dwelt upon by the counsel for the defence, but without success. Many of the vegetable poisons almost defy detection, except by the symptoms, _post-mortem_ appearances, and some experiments on animals of doubtful value. The detection of poison in the food taken, or in the vomited matters, is of great importance; but it is of still greater importance if it can be found in the urine, drawn from the bladder, this being a proof that it has passed through the system. Here again a caution is necessary--for it must be remembered that poisoning may be _feigned_ or _imputed_--the poison being mixed with the food and evacuations, and an innocent person accused. The following suggestions should be carefully considered by every analyst when substances are sent to him for examination: He should carefully note when and from whom the substances were received; in what state they were received--secured, or exposed--the number of articles, and whether properly labelled. He must make the analysis himself, and state where it was made. The character and nature of the substances examined should be noted, and he must be prepared to give an outline of the methods or processes used for their determination. He must also be able to guarantee the purity of his reagents, and be prepared to answer the following questions: 1. Is the poison free or combined? 2. What is the strength and quantity found? 3. Could the poisonous substance exist naturally? 4. How much of the poison found is a fatal dose? 5. If no poison is found, is there anything noxious or injurious to health? The analyst may have the following submitted to him for examination: (1) Substances found on the accused, or in the room, or on the person of the deceased. (2) Articles of food. (3) Vomited matters, urine, &c. (4) Contents of the stomach. (5) Solid organs of the body. He may also have his results called in question for the following reasons: (1) Purity of his reagents. (2) Faulty processes. (3) Hasty conclusions. (4) Experiments on animals. Death may undoubtedly be due to the action of a poison, and yet its presence may fail to be detected, due to--(1) The nature of the poison-strychnia, hydrocyanic acid, &c. (2) Vomiting and purging. (3) Absorption and elimination. (4) Decomposition--phosphorus, chloral hydrate, chloroform. (5) Smallness of the dose.