Mydaleine.—Composition not determined—from human corpses—actively poisonous.
Even after prolonged periods and with access of air, any putrefactive alkaloids which may form do so in very small quantities, and they are very unstable. In their chemical reactions they respond to many of the group-tests used for alkaloids, but they differ in their reaction to the special tests used for vegetable alkaloids. There is no test that will differentiate between putrefactive and vegetable alkaloids, as a class; at the same time no putrefactive alkaloid will give the same chemical reactions, and have the same physiological properties, as any one of the vegetable alkaloids.
Neurine was first obtained by Liebreich by boiling protagon with concentrated baryta. Since then it has been extracted from putrefying animal tissues. The free base is strongly alkaline, and gives a white cloud with the vapour of hydrochloric acid. It is intensely poisonous, resembling muscarine in its action. Very small quantities cause complete paralysis in frogs. Respiration ceases first, and the heart beats become more and more feeble, until it stops in diastole. If atropine be now injected the heart begins to beat again.
As a defence set up in cases of poisoning, when one or other of the rarer alkaloids has been used, it has been suggested that the poison discovered in the body of the deceased was due to the processes of putrefaction of the tissues themselves. In view of this it is important to know the toxic power of such putrefactive alkaloids as may be found in the human cadaver.
Two only of these are actively poisonous—neurine and mydaleine; others are toxic in so small a degree that large amounts would be required to produce lethal effects, far more in proportion to the body weight than any vegetable alkaloid for which it may be alleged they have been mistaken.
Neurine does not appear before the fifth or sixth day after death, mydaleine not until the seventh day, and only in traces; it does not appear in amount sufficient for quantitative analysis until the end of the second or third week.
At the period after death when a medico-legal analysis has generally to be made, choline is the only alkaloid present, and it is but feebly poisonous.
In rabbits neurine causes marked salivation and increased flow of secretion from the eyes and nose. The heart beats more quickly at first, but gradually slows down and stops in diastole. There is increased peristalsis of the intestines with profuse diarrhœa. There is narrowing of the pupil both after injection or local installation. Clonic spasms and violent convulsions occur, and are followed by paralysis first of the hind then of the fore legs, ending in death. The symptoms are prevented or relieved by atropine.
If atropine be injected first the poisonous effects of the neurine do not show themselves.
Mydaleine was discovered by Brieger in putrefying cadaveric organs. Small doses injected into guinea-pigs cause profuse lachrymation and coryza.