2. _Post-Mortem Appearances._--These in many poisons and classes of poisons are characteristic and unmistakable. The post-mortem appearances peculiar to the various poisons will be described in due course. 3. _Experiments on Animals._--These may be of value, but are not always conclusive. 4. _Chemical Analysis._--This is one of the most important forms of evidence, as a demonstration of the actual presence of a poison in the body carries immense weight. The poison may be discovered in the living person by testing the urine, the blood abstracted by bleeding, or the serum of a blister. In the dead body it may be found in the blood, muscles, viscera--especially the liver--and secretions. Its discovery in these cases must be taken as conclusive evidence of administration. If, however, it be found only in substances rejected or voided from the body, the evidence is not so conclusive, as it may be contended that the poison was introduced into or formed in the material examined after its rejection from the body, or if the quantity be very minute it will be argued that it is not sufficient to cause death. A poison may not be detected in the body, owing to defective methods, smallness of the dose required to cause death, or to its ejection by vomiting or its elimination by the excretions. 5. _Conduct of Suspected Persons._--A prisoner may be proved to have purchased poison, to have made a study of the properties and effects of poison, to have concocted medicines or prepared food for the deceased, to have made himself the sole attendant of the deceased, to have placed obstacles in the way of obtaining proper medical assistance, or to have removed substances which might have been examined. V.--SYMPTOMS AND POST-MORTEM APPEARANCES OF DIFFERENT CLASSES OF POISONS Whilst recognizing the fact that toxic agents cannot be accurately classified, the following grouping may for descriptive purposes be admitted with the view of saving needless repetition: 1. =Corrosives.=--Characterized by their destructive action on tissues with which they come in contact. The principal inorganic corrosives are the mineral acids, the caustic alkalies, and their carbonates; the organic are carbolic acid, strong solutions of oxalic acid, and acetic acid. _Symptoms._--Burning pain in mouth, throat, and gullet, strong acid, metallic or alkaline taste; retching and vomiting, the discharged matters containing shreds of mucus, blood, and the lining membrane of the passages. Inside of mouth corroded. There are also dysphagia, thirst, dyspnoea, small and frequent pulse, anxious expression, shock. Death may result from shock, destruction of the parts--_e.g._, perforation of stomach or duodenum, suffocation; or some weeks subsequently death may be due to cicatricial contraction of the gullet, stomach, or pylorus.