The heart poisons form a second class of acute poisons. The most important members of this group are digitalis, strophanthus, squills, dog bane, and lily of the valley. Poisoning by these substances is comparatively rare, although some of them are used by native tribes as arrow poisons (strophanthus) and employed in the killing of game and in warfare. The members of this group arc used extensively in medicine as heart tonics, and occasionally symptoms of poisoning result from over-doses. The most characteristic signs brought about by large closes or by concentrated smaller doses of these drugs are a marked reduction in pulse-rate, associated with a very high increase in arterial tension. Following this stage, if the drug is pushed, the heart is noticed to fail, the pulse becomes rapid, feeble, irregular, and convulsive, the pressure falls, and death may result. It is characteristic of this whole group of poisons that, when taken into the body, they are eliminated only after a considerable period of time. This leads to what is known as accumulation, and is always to he borne in mind when this class of drugs is administered, for by continued use of small doses a comparatively large accumulation is possible.
Another group of poisons, whose action is in more or less contrast with that discussed in the foregoing, is one in which aconite is the most important member. Others are veratrum, colchicum, lobelia, and larkspur. These drugs render the heart-beat slower in a manner somewhat similar to the digitalis group—namely, by stimulation of the cardiac regulating-centre in the medulla ; but they give rise to direct poisoning of the heart-substance and dilate the blood-vessels, bringing about a loss of tension in the arteries rather than an increase.
Symptoms of poisoning from aconite, which is one of the most important members of this class, and which is also an extremely acute and violent poison, are very characteristic. Aconite is not a very common plant in this country, but the larkspur, a near relative, causes very similar symptoms. The root of aconite has been confused with that of horseradish by the peasants who gather it in the countries in which it grows. The active principle of aconite is an alkaloid, aconitine, which is one of the most poisonous of all the alkaloids. The symptoms following the swallowing of a poisonous dose consist of a tingling in the mouth and pharynx, associated with a feeling of swelling of the lips and tongue, with burning and diminished sensibility. Then a peculiar sensation, as though ants were crawling over the skin, may be felt in the extremities ; and this sensation may even progress to loss of sensibility of the peripheral nerves.
These symptoms are followed by pain in the stomach, with excessive flow of saliva, nausea, vomiting, colic and and cold, clammy per spiration. The pulse-rate and respiration-rate sink, the former getting as
low as 35 to 45 per mintne, and the latter to to 15 ; and death may take place without much change in consciousness, although either delirium or coma may be present. The only method of treatment of poisoning by drugs of this class is by prompt evacuation of the contents of the stomach, the giving of hot water to aid elimination, and artificial respiration. Hot coffee is also useful.
In discussing this class of drugs it should not be forgotten that the very widely used preparation of larkspur, employed for insect parasites of the hair, gives symptoms similar to those of aconite, and should be treated in the same manner.
Poisons that act on the composition of the blood, whereby they enter into a more or less fixed combination with the haemoglobin and prevent the ordinary oxidising functions of this substance, furnish another very important group. To this belong a large number of widely used remedies, the most important of which are the different chlorates, and the nitrites, saltpetre being one of the most important. Nitroglycerine, amyl nitrite, nitrobenzol (widely employed in dyeing), aniline and the aniline dyes and derivatives, and particularly some of the newer drugs used to counteract pain, such as phenacetine, acetanilidc, and the numerous headache mixtures which contain this latter substance, such as phenalgine, antikamnia, ammonol, bromo seltzer, etc., etc., all belong to this class.
All these drugs, when taken into the body in sufficiently large doses, have the property of fixing the haemoglobin, resulting in the formation of meth moglobin ; and the characteristic symptoms are due to loss of the oxidising capacity of the blood, although there are individual variations in them all. Such drugs as amyl nitrite and nitroglycerine are much more rapid and powerful in their action than are the weaker aniline derivatives, such as phenacetine, acetanilide, etc.
The symptoms usually come on with a difficulty in respiration and with shortness of breath ; and the patient commences to feel cold and giddy, the skin becoming bluish, or even livid. With increased reduction of temperature the patient may suffer from chills. Other severe symptoms may then develop, such as loss of sensibility of the skin, great weakness of the muscles, and, finally, the characteristic convulsions and coma due to cyanosis. The treatment of poisoning by this class of drugs consists of prompt evacuation of the contents of the stomach and artificial respiration, which should be continued for some time.