Apoplexy, in the same way, is very like opium poisoning; and hydrophobia, lock-jaw, and even some cases of hysteria, closely resemble poisoning by strychnine.
Still, when a healthy man grows suddenly ill soon after a meal, the doctor keeps his eyes open, and if death follows he has a pretty shrewd idea of what caused it.
At all events, he feels perfectly justified in assuming that the case is not a normal one. He therefore hands over to the analyst the jars and other receptacles containing the portions of the subject's body likely to bear traces of the poison, knowing full well that if any poison is there the analyst will infallibly detect it.
The analyst begins by making a series of what may be called "brews," mincing, pounding, boiling, cooling, filtering, decanting, and distilling, over and over again. In these operations various solvents are used in succession, plain water separating out one class of poisons, alcohol dissolving out another group, benzol taking up a third, naphtha a fourth, ammonia a fifth, and so on. This preliminary work takes, not hours, but days to perform. At an early stage in it the operator discovers such volatile poisons as prussic acid, chloroform, carbolic acid, and phosphorus, if any of them be present. Later on he comes across the alkaloids, such as strychnine, digitalin, cantharidin, and other terrible poisons of that class.
Finally, the residue of the animal matter with which we have supposed the medical detective to be experimenting is mixed with hydrochloric acid, and distilled once again, after which it can contain no poison except one of the metals.
Thus, in the course of his examination, the analyst has made a number of decoctions, in one of which the poison is certain to be. In each decoction there may be any one of several groups of poisons.
In which is it, and what is it? After all this patient labour the solution is still far off. It may be a ptomaine from poisonous fish or decayed meat, a deadly berry, or leaf, or root, a small quantity of morphia, or phosphorus, or lead, or arsenic, or antimony.
Each brew is tested in turn. But, as illustrating the general procedure, take the last, which contains whatever metal may have had the fatal result. First, the chemist tests with "group reagents." He knows that if he puts into the glass containing the last brew certain bodies in succession, some metals, if they are there, cannot be kept from rushing into the arms of one, others will as passionately embrace another, others still will unite with a third, while some will always repudiate any alliance. There are in all cases signs of the union, when it takes place, such as a blue or white or red colour, or a powder falling to the bottom, or a fizzing of escaping gas.
In practice the analyst puts a little of the brew in a small glass test-tube, pours in some distilled water, and carefully drops in some hydrochloric acid. Now, if there is either silver, mercury, or lead, in the brew, down goes a white powder; if none of these things is there, no change follows.
Next he adds some sulphuretted hydrogen water, a sort of aerated water smelling of rotten eggs. If tin, platinum, bismuth, cadmium, arsenic, or one of several other metals, is in the brew, a coloured powder falls to the bottom. Should nothing occur, he adds other things, until he has tested for five groups of metals.