A text-book of pharmacology and therapeutics; or, The action of drugs in health and disease, . y asstrychnine, though small doses may act on the brain, for they oftenelicit restlessness and timidity without any marked change in the reflexexcitahility. The centres in the medulla oblongata are also involvedin the effects, as is indicated by acceleration of the breathing and occa-sionally by some slowness of the pulse from action on the pneumogastriccentre. Frogs show no nervous symptoms that cannot be ascribed to actionon the spinal cord, and in some species these are elicited with con-sitlerabl
A text-book of pharmacology and therapeutics; or, The action of drugs in health and disease, . y asstrychnine, though small doses may act on the brain, for they oftenelicit restlessness and timidity without any marked change in the reflexexcitahility. The centres in the medulla oblongata are also involvedin the effects, as is indicated by acceleration of the breathing and occa-sionally by some slowness of the pulse from action on the pneumogastriccentre. Frogs show no nervous symptoms that cannot be ascribed to actionon the spinal cord, and in some species these are elicited with con-sitlerable difficulty owing to the muscular action described below. On comparing the effects of caffeine and strychnine on the centralnervous system, it will be found that while there is a general similarityin their action, the latter causes more marked stimulation of the lowerdivisions and has less action on the cerebrum in mammals and both produce a general increase in the activity of nerve cells,but caffeine acts more on the psychical, strychnine more on the reflexfunctions. Fig. 19 I 1. A muscular fibre of tlie frog (highly magnified). -1, normal; B, after the applicationof caffeine solution. The coarse striiB in B are the folds of the sarcolemma. Theophylline resembles caffeine in its action on the central nervoussystem, while theobromine induces few or no symptoms of monomethyl-xanthines and xanthine itself stimulate the centralnervous system in the frog (Schmiedeberg). The Muscular action of caffeine is best seen in the Hana temj)oraria(grass frogj, although it is also induced in other sj)ecies of frogs, andsome rigidity may be elicited in mammals by very large doses. ^Vhena few drops of caffeine are injected into the leg of a frog there followsa peculiar stiffness and hardness in the muscles around the point ofinjection, which slowly sj^reads to other ])arts of the body and inducesthe appearance of rigor mortis. The same effect is observed whenteased mus
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