Casali (Gazetta, 1881, 312) regards ptomaines as not true alkaloids, but as “acid or basic amidated compounds.” It is only the basic ones that will interfere with testing. Panum and Bergmann have isolated a substance called “sepsin,” generated by putrefaction, poisonous, acting like a ferment but not destroyed by boiling, soluble in water, but insoluble in alcohol, and thereby distinguished from alkaloids. Sonnenschein and Zuelzer found a product of putrefaction which produced tetanic symptoms, besides one resembling atropine. But these substances, or similar ones, can be produced without putrefaction, as Paterno and Spica have shown that fresh blood and fresh albumen (white of egg) yielded, with phosphomolybdic acid, potassio-mercuric iodide, and other alkaloidal reagents, precipitates like those of the vegetal alkaloids. Selmi has even supposed that death from various diseases may be due to the formation of these compounds. The same author obtained from a dead body one month after death a considerable amount of a crystallizable ptomaine, giving reactions like those of alkaloidal poisons, and having poisonous effects on frogs.
Brouardel and Bouting (Compt. Rend. 92, 1056) propose the reducing action of ptomaines as a distinction between them and vegetal alkaloids. The solution in weak acid is added to a dilute mixture of ferric chloride and potassium ferricyanide: the latter, if a ptomaine be present, is reduced to ferrocyanide, and Prussian blue is thereby precipitated. But Spica (Gazetta, 11, 486) has shown that strychnia, brucia, morphia, and some others produce this reaction readily, and Beckurts (Arch. Pharm. 3, 20, 104) adds aconitine and others as producing it slowly. Hence the distinction is delusive. See also Husemann (Arch. Pharm. 3, 16, 169; also 3, 20, 270), Tauret (Compt. Rend. 92, 1163).
The discovery of these bodies has certainly raised a new difficulty for toxicologists, and suggested a new and plausible defence, as it must be confessed that at present there is no general method of distinguishing between “cadaveric” and vegetal alkaloids. Yet this mainly affects the “physiological” tests—on frogs and other small animals—for there is no ptomaine yet discovered which gives all the reactions of strychnia, morphia, &c. If a chemist be asked, “Could any other substance produce these reactions?” he can only answer, “I do not know of any”; he cannot aver the impossibility. Then the circumstantial evidence must decide.
In conclusion, the following principles should be noted:—
1. The quantity of poison found is generally only a small fraction of the quantity taken. The vomit and evacuations are frequently lost, and much may be decomposed by vital actions in the body, or by putrefaction. That which has caused death is probably thereby either decomposed or so combined as to be rendered undetectible: that which is found is merely the surplus beyond the fatal dose. This would account for the frequent non-discovery in the tissues when a small amount has been given, or much time has elapsed. To metallic poisons this does not apply, as, unless eliminated, they can always be found. See further under Strychnia.
2. The symptoms will differ according to the dose, the form (solid or solution, pure or admixed), habit, or idiosyncrasy, the state of health, &c.
3. In the post-mortem examination, appearances common to dead bodies generally are often mistaken for the effects of poison. See Casper’s Handbook, vol. I., et passim.
4. Unhealthy or improper food or acute disease may cause suspicious symptoms. This is the commonest solution of suspected poisoning.
5. In experiments on animals, it may be objected that they are inconclusive as to man. This is not strictly true. But if a recent vomit proves poisonous to an animal, with the same symptoms as in the man, that is almost conclusive evidence.