Effects of alkaloids, anaesthetics and poisons on plant motion and protoplasmic streaming

Darwin's Insectivorous Plants (1875) lists these agents in a chapter synopsis. It names strychnine salts, quinine, digitaline, nicotine, curare, morphia and cobra poison among others. He reports that sulphate of quinine does not soon arrest the movement of the protoplasm¹. Cobra poison apparently accelerates it². Of the alkaloids and their salts tried, several had no power of inducing inflection. Others were absorbed, as the changed colour of the glands showed, but acted only moderately. The acetate of quinine and digitaline caused strong inflection³. The effect therefore varied from one alkaloid to the next.

Verworn (1899) set these agents against chemical stimuli and called them narcotics or anaesthetics. Alcohol, ether, chloroform and chloral hydrate depress all forms of living substance. The alkaloids, including morphine, quinine, veratrine, digitaline, strychnine and curare, form a second group. Some act on many kinds of cell. Others affect specific cells only, especially those of the central nervous system⁴. Sherrington (1906) used strychnine differently. He reported that it converts a central inhibition into excitation, and he argued that this makes simultaneous excitation of antagonistic muscles in willed actions easier to understand⁵.

Bayliss (1915) described Langley's work of 1906 on nicotine and curare. In large doses nicotine acts like curare and stops nerve excitation from reaching the muscle substance⁶. Hill (1926) reported that the Lapicques found curare raises the chronaxie of muscle, so the usual nerve impulse no longer stimulates it. He and Hartree found that curare increases the heat produced by a single shock. They suggested that it may prolong the rise of permeability that follows the stimulus⁷. Bayliss reports that 10 to 15 mg of nicotine suffices in the fowl.

Reid (2023) reviewed work by Boisseau and colleagues (2016) on Physarum. Plasmodia separated from food by a quinine-agar bridge showed clear aversion. Over 5 days they reduced that response. Quinine-habituated plasmodia did not lessen their aversion to caffeine, and the reverse also held. The specificity ruled out fatigue and general sensory adaptation⁸. Kippenberger and colleagues (2023) found a different result with propofol. Physarum did not habituate to propofol-soaked food⁹. They cite earlier work in which Physarum habituates to sodium chloride when it is repeatedly rewarded with food after crossing a barrier with sodium chloride.