This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
Gastro-intestinal tract. - Being intensely bitter, nux vomica is a good stomachic, increasing the vascularity of the gastric mucous membrane, the secretion of gastric juice, and the movements of the stomach, just like calumba, gentian, or any other bitter; consequently it aids digestion and sharpens the appetite. In the intestine it is a direct stimulant to the intestinal muscular coat, and by this means it increases peristalsis, and is therefore purgative.
Blood. - Strychnine is absorbed into the blood, and circulates as such. If blood is mixed with strychnine and shaken with air, it contains more oxygen and less carbon dioxide than it would have done had the strychnine been absent; but there is no evidence that strychnine in small doses alters the oxidizing power of living blood.
Spinal cord. - Strychnine causes convulsions. They are not cerebral, for they occur if the spinal cord is separated from the brain. They do not depend upon excitation of the motor nerves or muscles, for they are absent in a limb the spinal anterior nerve-roots of which are cut. They occur if the posterior nerve-roots are cut, provided the proximal end is stimulated. Therefore they must be spinal; and this is proved by the fact that if all the vessels of the lower part of the spinal cord are ligated just at their entry into the cord, so that this is the only part of the body deprived of its blood supply, and strychnine is injected into the blood, convulsions occur in all the muscles except those the nerves of which spring from the part of the cord which the strychnine cannot reach. Again, if an animal be convulsed by strychnine, and a probe be slowly passed down the spinal canal, the convulsions will gradually cease from above downwards. But a peripheral stimulus, particularly if sharp and sudden, so easily excites convulsions when strychnine has been given that we are justified in assuming that every convulsion is excited by a peripheral stimulus, and often so slight as not to be evident. Further, strychnine enormously exaggerates the conduction power of the cord in such a way that general convulsions reflexly follow a very slight local stimulus. It is believed that the precise part of the spinal cord stimulated to increased excitability by strychnine is that immediately on the afferent side of the anterior cornual cells.
Muscles and nerves. - Even with enormous doses the muscles and afferent nerves are unaffected. Towards the end of a case of poisoning the functional activity of the motor end-organs is depressed. This is due to direct action on them, and occurs readily in some species of frogs.
Brain. - The convolutions are quite unaffected. The centres in the medulla, which are really the continuation upwards of the anterior cornua of the cord, are powerfully stimulated, especially the respiratory centre. The vaso-motor centre is also considerably excited, and chiefly for this reason the blood-pressure rises from the very first. The cardiac centre is but slightly affected although the clinical evidence is in favor of its being strongly influenced.
Circulation. - Strychnine stimulates the heart directly, either by its action on the cardiac muscles or, as most authorities think, by stimulating the motor ganglia. The blood-pressure is raised, partly no doubt by the action on the heart, but also by the contraction of the vessels all over the body, which is brought about first by the direct excitation, by the strychnine, of the medullary vaso-motor centre, and subsequently by its asphyx-ial stimulation, and also by the increased peripheral resistance which must occur from the frequent contraction of all the muscles. The result is that the force of the heart is increased and the diastole lengthened.
Respiration. - Respiration is rendered quicker and deeper because strychnine excites the spinal and medullary respiratory centres. The respiratory muscles are implicated in the general convulsions with the result that the patient ultimately becomes asphyxiated owing to exhaustion of them, and to their prolonged contraction during the convulsive spasms. The heart continues to beat after death which is entirely due to failure of respiration. The excessive muscular contractions occasionally cause a rise of temperature, but so rarely that often the loss of heat must be greatly increased.
Special senses. - Smell, hearing, touch and sight are sharpened by strychnine. The field of vision, especially for blue, is said to be enlarged.
Elimination. - Strychnine is eliminated unchanged in the urine. It is excreted very slowly, and therefore accumulates in the system. Tolerance is never established. For a clinical account of strychnine poisoning see Toxicology.
Brucine and thebaine act like strychnine, but methyl-bru-cine, methyl-thebaine, and methyl-strychnine do not influence the cord, but paralyze the ends of the motor nerves like curare.
Strychnine acts on all animals in the main as on man; but some birds and guinea-pigs are less susceptible to it, for they absorb it slowly.