1. Evidence from the Symptoms.—As a general rule the symptoms come on suddenly while the person is in apparent health, except in cases of slow poisoning, when the poison may be so administered by frequently repeated and small doses as to simulate disease, and the physician is more easily misled than when a single large dose is given. In cases of suspected homicide this suddenness in the accession of the symptoms is particularly to be noticed, and we may have to decide as to the probabilities of accident, suicide, or homicide. Here collateral evidence must be our guide. The slowness, obscurity, and irregularity of the symptoms are more in favour of homicide than either accident or suicide. But it must also be borne in mind that the invasion of many diseases is sudden, as is the case with cholera, gastritis, and some others.
Certain conditions of the system more or less modify the effects of some poisons. Thus, sleep delays the action of arsenic; and this may also be the case with other poisons. Intoxication has also been said to exert a retarding power over the action of certain poisons. This is probably more apparent than real, the fact being that the symptoms in the cases observed are masked.
Much more important, however, is the influence of disease. Large doses of opium are well borne in mania, delirium tremens, dysentery, and tetanus; whereas it is well known that even small doses of mercury in cases of Bright‘s disease of the kidney, or in children recovering from any of the eruptive fevers, have produced dangerous salivation.
The symptoms of poisoning go on from bad to worse in a steady course; but there may be remissions, followed, under treatment, by their entire disappearance, no ill effect remaining. Remissions are most likely to occur in slow poisoning with the metallic irritants, from fear of detection or cunning on the part of the poisoner to imitate the progress of disease. In nervous affections, all the symptoms must be taken into consideration, and these will be found to differ from those of any known poison. The history of the case should also have due attention paid to it.
In poisoning, the symptoms appear soon after food or drink has been taken. This is open to the objection that apoplexy has occurred immediately after a meal. The probative value of the above statement is, however, increased if several persons have been similarly affected after partaking of the same dish, especially if the symptoms followed within a short time—under four hours—of the meal. But it must also be remembered that all persons are not affected alike by the same poison. Again, the diagnostic value is weakened if it can be proved that the person or persons affected have taken nothing in the way of food for two or three hours previously.
The flesh of animals poisoned by accident, or intentionally, may seriously affect those who eat it.—As a case in point may be mentioned the injurious effects produced in some persons who had partaken of the Canadian partridges imported to this country some years ago, and which had probably eaten some poisonous berries during the severe winter of that year.
Poisons may be introduced into the system otherwise than by the mouth; that is, they may be placed in the vagina or rectum, or inhaled when volatile poisons are used. Sometimes a poison has been introduced into the medicine, or a poisonous draught substituted for the one prescribed. In any case, where suspicious symptoms suddenly occur, the poison has most probably been taken in from half an hour to an hour previously, and it is of special importance to note the period of time that may have elapsed between the accession of the symptoms and the last meal, or administration of medicine.
When called in to a case of suspected poisoning, and in many cases where no suspicion at the time arises, the medical attendant should pay attention to the following points:
1. The time of the occurrence of the symptoms, and their character.
2. The time that has elapsed between their commencement and the last meal, dose of medicine, &c.