MODE OF ACTION I. LOCAL 1. Corrosion of the part } to which the poison } Strong acid, alkali, &c. is applied. } 2. Inflammation as the } result of irritants } Arsenic, cantharides, &c. applied to a part. } 3. Effects on the nerves } Dilatation of the pupil by belladonna, of motion and sensation. } tingling of the tongue and skin by } aconite, paralysis by conium. II. REMOTE 1. Common--not to be distinguished from the effects of injury or disease. 2. Specific--peculiar to the poison itself. (1) General--affecting the whole system.--Antimony. (2) Partial--acting on a particular organ.--Antimony. MODIFYING CAUSES { 1. Quantity of the poison increases its rapidly { fatal action. { 1. Quantity. { 2. Action changed by the size of the dose. Thus, { oxalic acid in large doses acts as a corrosive; { in small doses on the heart, brain, or spinal { cord. { _Solubility_ increases the activity of poisons. { _Chemical Combinations._--Baryta is poisonous, 2. Form. { sulphate of baryta is inert. { _Mixture._--Dilution may retard or accelerate { the action of a poison.[19] 3. Point of application--Skin, lungs, mucous and serous membranes. { _Habit_--generally lessens the action of { poisons, e.g. _arsenic-eater, morphine-taker_. 4. Condition of { _Idiosyncrasy_--increases or may lessen the the body. { action of poisons. { _Disease_--generally lessens, but in some cases { increases the action of poisons. [19] Dilution lessens the activity of some poisons, by prolonging the time necessary for their absorption; but in the case of powerful irritants, which act through the blood, moderate dilution increases their activity, by enabling them to enter the vessels more easily. Oxalic acid is an example of the effect of dilution as a modifying agent in its action. A small concentrated dose acts as an irritant; diluted, it is soon absorbed, and quickly causes death. GENERAL EVIDENCE AND DIAGNOSIS OF POISONING It will now be necessary to consider briefly the general evidences of poisoning, in order to determine whether a death alleged to be due to poison is not really the result of disease. For convenience of description, this subject will be divided into five sections: 1. Evidence from the Symptoms. 2. Evidence from the _Post-mortem_ Appearances. 3. Evidence from Chemical Analysis. 4. Evidence from Experiments on Animals. 5. Moral Evidence.