1. Toxic doses taken by the mouth or given by subcutaneous injection give rise to strong dilatation; this vanishes before death, giving place to moderate contraction. This form is due to stimulation of the dilatation centre, later passing into paralysis. An example is found in the action of aconite.
2. After subcutaneous or local application, a dilatation neutralised by physostigmine in moderate doses. This is characteristic of β-tetrahydronaphthylamine.
3. After subcutaneous injection, or if applied locally in very small doses, dilatation occurs persisting to death. Large doses of physostigmine neutralise the dilatation, but it is not influenced by muscarine or pilocarpine: this form is characteristic of atropine, and it has been called mydriasis paralytica periphera.
The heart at the height of the poisoning stops in systole.
2. Arrest in systole.—The systole preceding the arrest is far stronger than normal, the ventricle often contracting up into a little lump. Contraction of this kind is specially to be seen in poisoning by digitalis. In poisoning by digitalis the ventricle is arrested before the auricle; in muscarine poisoning the auricle stops before the ventricle. If the reservoir of Williams’ apparatus is raised so as to increase the pressure within the ventricle the beat may be restored for a time, to again cease.
A frog’s heart under the influence of any poison may be finally divided into pieces so as to ascertain if any parts still contract; the significance of this is, that the particular ganglion supplying that portion of the heart has not been affected: the chief ganglia to be looked for are Remak’s, on the boundary of the sinus and auricle; Ludwig’s, on the auricle and the septum of the auricle; Bidder’s, on the atrioventricular border, especially in the valves; and Dogiel’s ganglion, between the muscular fibres. According to Dogiel, poisons acting like muscarine affect every portion of the heart, and atropine restores the contractile power of every portion.
VI.—General Method of Procedure in Searching for Poison.
§ 31. Mineral substances, or liquids containing only inorganic matters, can cause no possible difficulty to any one who is practised in analytical investigation; but the substances which exercise the skill of the expert are organic fluids or solids.
The first thing to be done is to note accurately the manner in which the samples have been packed, whether the seals have been tampered with, whether the vessels or wrappers themselves are likely to have contaminated the articles sent; and then to make a very careful observation of the appearance, smell, colour, and reaction of the matters, not forgetting to take the weight, if solid—the volume, if liquid. All these are obvious precautions, requiring no particular directions.