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:
| Physiological. |  | Dilatation of the pupil in poisoning by | |
| belladonna, hyoscyamus, &c. | |||
| Contraction of the pupil in poisoning by | |||
| opium, Calabar bean. | |||
| Physical. |  | Taste.— | Bitter taste of the secretions. Strychnia, |
| picrotoxin. The milk of animals fed on wormwood | |||
| may become bitter; on colchicum, 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.
| MODE OF ACTION | ||
|---|---|---|
| I. LOCAL | ||
| 1. Corrosion of the part |  | Strong acid, alkali, &c. |
| to which the poison | ||
| is applied. | ||
| 2. Inflammation as the | | Arsenic, cantharides, &c. |
| result of irritants | ||
| 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. |  | 1. Quantity of the poison increases its rapidly |
| fatal action. | ||
| 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. | ||
| 2. Form. | | Solubility increases the activity of poisons. |
| Chemical Combinations.—Baryta is poisonous, | ||
| 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. | ||
| 4. Condition of the body. | | Habit—generally lessens the action of |
| poisons, e.g. arsenic-eater, morphine | ||
| taker, morphine taker. | ||
| Idiosyncrasy—increases or may lessen the | ||
| action of poisons. | ||
| Disease—generally lessens, but in some | ||
| cases increases the action of poisons. | ||
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.