[384] Hermann’s Lehrbuch der exper. Toxicologie, p. 374.
§ 357. Physiological Action.—From experiments on animals, the essential action of morphine on the nervous and arterial systems has in some measure been examined. There is no very considerable action on the heart. The beats are first accelerated, then diminished in frequency; but very large doses introduced directly into the circulation at once diminish the pulsations, and no acceleration is noticed. The slowing may go on to heart-paralysis. The slowing is central in its origin, for on the vagi being cut, morphine always quickens. With regard to the peripheric ends of the vagi, small doses excite, large paralyse. If all the nerves going to the heart are divided, there is first a considerable acceleration, and then a slowing and weakening of the pulsations. The arterial blood-pressure, at first increased, is afterwards diminished. This increase of blood-pressure is noticed during the acceleration of the pulse, and also during some portion of the time during which the pulse is slowed. Stockman and D. B. Dott,[385] experimenting on rabbits and frogs, consider that a medium dose of morphine first of all depresses the spinal cord and then excites it, for tetanus follows. If morphine is in sufficient quantity thrown into the circulation then tetanus at once occurs. It would thus appear that depression and stimulation is entirely a matter of dosage. Gescheidlen, in his researches on the frog, found the motor nerves at first excited, and then depressed. When the doses were large, there was scarcely any excitement, but the reverse effect, in the neighbourhood of the place of application. According to other observers, the function of the motor nerves may be annihilated.[386] According to Meihuizen, reflex action, at first much diminished, is later, after several hours, normal, and later still again increased. The intestinal movements are transitorily increased. In the dog there has been noticed a greater flow of saliva than usual, and the flow of bile from the gall-bladder is diminished. The pupils in animals are mostly contracted, but, if convulsions occur towards death, they are dilated.
[385] Brit. Med. Journ. (2), 1890, 189-192.
[386] Arch. f. d. Ges. Physiol., vii. p. 201.
§ 358. Physiological Effect of Morphine Derivatives.—By introducing methyl, or amyl, or ethyl, into the morphine molecule, the narcotic action is diminished, while the tetanic effects are increased. Acetyl, diacetyl, benzoyl, and dibenzoyl morphine, morphine sulphuric ether, and nitrosomorphine are all weaker narcotics than morphine, but, on the other hand, they depress the functions of the spinal cord and bring on, in large doses, tetanus.
The introduction of two methyl groups into morphine, as in metho-codeine, C17H17MeNO(OH)-Me, entirely alters the physiological effect. This compound has an action on voluntary muscle causing gradual paralysis.
The chlorine derivatives, trichlormorphine and chlorcodeine, have the characteristic action of the morphine group on the central nervous system and, in addition, act energetically as muscle poisons, soon destroying the contractile power of the voluntary muscles with which they first come into contact at the place of injection, and more gradually affecting the other muscles of the body.[387]