We know not the cause, but certain poisons appear to select a particular route for their exit--thus iodide of potassium leaves by the urine; mercury and its salts by the saliva; arsenic and eserine, the active principle of the Calabar bean, in small quantities, by the stomach, &c. We are, however, prepared to show that all poisons must enter the blood before they produce their effects, and that almost simultaneously with the entrance of the poison into the blood a process of elimination begins, and that fatal effects depend upon absorption taking place more rapidly than elimination. On the amount also of the poison absorbed do its fatal effects depend, and not on the quantity actually taken. Whilst absorption and elimination are both going on, some of the poison is being deposited in the organs and tissues of the body. As proofs of these statements it has been shown that poisons have been detected in the blood, and that urine, saliva, and milk, fluids secreted from it, may contain portions of the poison taken, and produce dangerous symptoms when given to other animals. Poisons applied to the brain tissue, or to nerve trunks, do not produce symptoms, and the action of a poison may be arrested for a time by compressing by a ligature the main vessels of the limb under the skin of which the poison has been injected. After death no trace of the poison may be detected, the quantity taken being just sufficient to produce a fatal result, or elimination may be so rapid that, although death was directly due to the poison, any remains of its existence cannot be made out. This occurred in the case of Dr. Alexander, who died from an accidental dose of arsenic, all the arsenic being eliminated in _seventeen_ days--in another fatal case, in _seven_ days. (Taylor) As evidence of the diffusion of poisons the following table may be of use: { Dilatation of the pupil in poisoning by Physiological. { belladonna, hyoscyamus, &c. { Contraction of the pupil in poisoning by opium, { Calabar bean. { _Taste._--Bitter taste of the secretions. Strychnia, { picrotoxin. The milk of animals fed on wormwood { may become bitter; on colchicum, Physical. { poisonous. { { _Smell._--Prussic acid, tobacco, conium, &c. { { _Colour._--Skin blackened by nitrate of silver, { given internally. _N.B._--By the aid of the spectroscope the salts of lithium and thalium have been detected in the liver and other tissues. Recapitulation of the Mode of Action of Poisons, and the Causes which Modify their Action.