With those in Part I. a registration of the sale is compulsory, the purchaser must be known to or introduced by some person known to the vendor, and the purpose for which the poison is required, the date, the name and amount of the poison sold, the name and address of the buyer, and the entry must be signed by the purchaser and introducer. All substances in Parts I. and II. must be labelled by the vendor with a label bearing the name of the poison, the name and address of the seller, and the word “Poison”; but with those in Part II. no registration as in Part I. is required. In the sale of arsenic both the seller and purchaser must sign the entry, and the introducer must witness it. No arsenic can be legally sold to a person under the age of twenty-one years; nor may it be sold in quantities of less than 10 lbs. unless mixed with soot or indigo—one ounce of the former, or half an ounce of the latter, to each pound of arsenic. If quantities of over 10 lbs. be sold, and the soot or indigo would render it unfit for use in the way desired, then they may be omitted (Arsenic Act, 1851).
Classification of Poisons.—A good and scientific classification of poisons is still wanted. The following simple general division, depending upon the chief effect, may be taken as guides by the student:
| (a) Corrosives—Local corrosion. | ||
| (b) Irritants—Gastro-intestinal irritation. | ||
| (c) Neurotics—Altered action of the nervous system. | ||
| 1. INORGANIC | ||
| Corrosive—Sulphuric acid, &c. | ||
| Irritant—Arsenic, &c. | ||
| 2. ORGANIC | ||
| Irritant—Savin, Cantharides. | ||
| Affecting Brain—Opium. | ||
| Affecting Spinal Cord—Strychnia. | ||
| Affecting Heart—Digitalis. | ||
| Affecting Lungs—Carbonic acid. | ||
| (Guy.) | ||
| IRRITANTS | ||
| Mineral |  | Acid poisons—Sulphuric acid, &c. |
| Alkaline poisons—Caustic soda, &c. | ||
| Non-metallic—Phosphorus, Iodine, &c. | ||
| Metallic—Arsenic, Antimony, &c. | ||
| Vegetable—Savin, Elaterium, &c. | ||
| Animal—Cantharides. | ||
| NEUROTICS | ||
| Cerebral—Opium, Hydrocyanic acid, Alcohol. | ||
| Spinal—Strychnia, Nux vomica. | ||
| Cerebro-spinal—Conium, Belladonna, Aconite. | ||
| Cerebro-cardiac—Calabar bean, Digitalis. | ||
| (Taylor.) | ||
The subjoined classification is based upon that adopted by the late Professor Sir Douglas Maclagan. Where the poison acts in such a manner as to place it in two or more groups, I have fully described it in one, merely drawing attention to it under the others:
Action of Poisons.—Amid the difficulties which surround this subject, three points appear to have been clearly made out: (1) That it is necessary for all poisons to enter the blood before their specific action can be produced. (2) That poisons possess an elective affinity for certain tissues and organs. Thus, arsenic, however introduced into the system, as a rule attacks the stomach; and this peculiarity of action closely allies it to the poisons of typhoid, scarlet fever, smallpox, &c., which appear to have, respectively, an elective affinity for the glands of the intestines, the throat, and the skin. (3) That the habitual use of a poison in medicinal doses does not ensure a perfect toleration on the part of the system with regard to the action of the poison, for sooner or later a complete cachexia is produced, showing that the poisonous effect of the drug is not arrested.
Besides the above, there are also certain conditions connected with the action of poisons: (1) The poison is absorbed and distributed by the blood. (2) A portion is eliminated by the fluid secretions and excretions. (3) Another portion is for a time deposited in the tissues and organs of the body. These processes are of necessity simultaneous.
The channels of entrance and exit are as follows: Of entrance we have—(1) The blood-vessels as a result of wounds—more important in a physiological than a medico-legal question. (2) The skin and cellular membrane.—Absorption by the skin is modified by the condition of the part, and also by the form in which the drug is applied. Thus the skin of the arm-pits and groins is more absorbent than the palms of the hands. Watery solutions are not so effective as oily preparations, and the application of the drug in fine powder is more effectual than a watery solution of it. This is explained by the presence of a natural oily, unctuous substance on the skin, which prevents the direct contact of the watery solution, but if the solution be allowed to evaporate on the part, the substance thus left in minute division is then readily absorbed. The danger of allowing strong solutions of corrosive sublimate to evaporate on the head in the treatment of certain skin eruptions is thus explained. (3) The lungs and air-passages.—Absorption by these organs is most active, hence the intense rapidity in the action of aerial poisons. (4) The stomach and intestines.—Poisons introduced into the stomach or intestines take longer to arrive at the special organs on which they act than by the other channels of entrance. They are absorbed by the capillaries into the mesenteric veins, and before passing to the heart, by which they enter the general circulation, they pass through the liver, where they are in part excreted in the bile or deposited in the gland. The absorbing power of the stomach is modified by its fulness or emptiness, and poisons not soluble in water may be rendered so by the gastric secretion.
The avenue of entrance may materially modify the action, and some poisons which act rapidly when entering by a wound, are inert when taken into the stomach. Snake poisons when given by the mouth are entirely harmless. Hydrogen sulphide is more toxic when inhaled than when taken in solution. This, though true in some cases, does not always occur; and the inertness of these poisons, it has been suggested, may be due to the elimination of them being as rapid as their absorption, so that a poisonous dose never enters the circulation. The intestines absorb more rapidly than the stomach, and this must be borne in mind when administering powerful drugs per anum.
Of the channels of exit we have: (1) The kidneys. (2) The lungs. (3) The bile. (4) The milk. (5) The saliva. (6) Mucous membrane. (7) The skin.