A fern petiole, a hard sheath you crack open with care, then pull apart in both directions. What comes out is a long, soft, white filament. Bose puts it this way, page 468: “I was able to isolate the conducting fibro-vascular threads, which were long, soft, and white in colour, remarkably similar in their appearance to animal nerves.” The species are named, the common maidenhair and Nephrodium molle, and the filament sometimes reaches twenty centimetres. Thirty minutes in physiological saline to erase the excitation from handling, iced saline if the weather is warm, a moist chamber compulsory, otherwise you watch the excitability rise sharply and then die out for good. These are the exact precautions you take with a frog nerve.
This is the central gesture of Comparative Electro-Physiology, a volume of seven hundred and thirty-four pages, published in London by Longmans in 1907, forty-eight chapters, four hundred and six figures, and a classified list of three hundred and twenty-one numbered experiments at the end of the volume. The French edition (Électrophysiologie comparée), the one I read, appears twenty years later from Gauthier-Villars, 55 quai des Grands-Augustins, translated by Dr Pierre Lehmann. The publisher is Poincaré’s. So Bose was not shelved in France under curiosities.
What the book contains
The preface, dated Calcutta, August 1906, announces the plan and justifies it: “my mode of investigation has thus been determined by the necessary progression from simple to complex”. You start from the molecular response of matter, you move up to the plant, then to the animal, then to the psychic. It is the exact reverse of the 1902 book, where Bose came down from animal muscle to a tin wire.
Six blocks stand out. The first eight chapters lay the foundations, the electromotive response of plants and the conditions for quantifying it. Chapters IX to XVIII deal with anisotropy and death. Chapters XIX to XXVI form the strangest part, the leaf considered as an electric organ, the skins, the glands, digestion, sap. Then come light and the retina, then ten chapters on the nerve, which are the heart of the book. The last ones take up sensation, memory, and draw the conclusions.
Each chapter opens with a one-sentence summary listing everything that follows, and the final classified list sorts the 321 experiments by family with page references. Reading the forty-eight summaries in a row gives you the complete map. The book is difficult, but it can be worked through.
The instruments, and what they yield
The 1902 volume rested on four devices. This one has a dozen, several of them bearing names coined from Sanskrit. The Kunchangraph comes from kunchan, contraction. The Shoshungraph records suction, with a pen following the water index of a potometer tube, and a compensator that lets water in at exactly the rate the plant draws it, so that the curve becomes horizontal and the slightest deviation can be read. The Morograph traces a curve while the tissue is continuously heated. The rheotome, modified from Bernstein, solves a problem of method: the galvanometer is too slow for the real variation, so Bose short-circuits it permanently and brings it into circuit for only a hundredth of a second, at an adjustable interval after the stimulus, then reconstructs the true curve point by point.
The thermal stimulator is the methodological find of the book. A platinum wire surrounds the tissue without touching it, brought to red heat for half a second. Constant current, constant duration, therefore constant stimulus. And above all, when you want to measure an electrical response, you do not stimulate electrically.
The figures then arrive with a sharpness that comes as a surprise. The death point, chapter XVI, is determined on twenty-four specimens by four independent methods, the flower that opens or closes, the Morograph on styles of Datura and Hibiscus, electrical inversion on a cauliflower petiole, the sign reversal of the response. Everything converges between 59 and 60 degrees. Bose himself is astonished, “it is in the highest degree remarkable that the points of inversion… should so exactly coincide”, and he shows that this point drops to 53 degrees when the plant comes out of a cold spell. A weakened plant dies sooner, and the measurement says so.
The table of transmission speeds is made to be seen. Anodonta nerve, 10 mm per second. Eledone nerve, between 0.5 and 1. Mimosa petiole, 14. Gourd tendril, 5. And the isolated fern nerve, 50. Five times faster than the mollusc. The modifiers are measured one by one on Biophytum, the intensity of the stimulus, fatigue, temperature which takes the speed from 3.7 to 9.1 mm per second between 30 and 37 degrees, and direction, centripetal and centrifugal always differing slightly. Another figure, more telling still: a single thermal shock of less than a second is enough to make the isolated nerve respond, where the whole petiole of the same fern needs a score of them for a limp response.
Then there are the experiments you hardly know what to do with, and which you never forget. Bose puts grape skin, tomato skin, frog skin, the skin of a tortoise’s neck, gecko skin and intact human skin under the same apparatus, and concludes that they do not essentially differ. He records a fresh Nepenthes pitcher, then another containing captured insects, and compares them with a frog’s stomach. He measures the duration of after-images on his own retina, 3 seconds at eight in the morning, 5 seconds at three in the afternoon, 6.5 seconds at eleven at night, and reads in it the fatigue of his day. He wires a telephone into the circuit of his tongue, speaks into it, obtains a lingual current, and notes the thing down with an exclamation mark, “surely a curious instance of the speech of one inducing lingual response in another”.
The ideas, and the place where they give way
Bose himself lists his five breaks with received doctrine. The continuity of tissues against their specificity. The motile nerve against the nerve held to be immobile. Plants capable of conducting a true excitation. Pflüger’s law wrong outside a certain range. And the nerve impulse not simple but double, which would ground the two tonalities of sensation.
His energetic thesis is worth keeping, because it takes aim at the dominant image of his time, the gunshot released by the trigger. He answers that the plant is not consumed by the ceaseless stimuli of its surroundings, and that “it is the energy of the environment which is the agent that fashions the microscopic embryo into the gigantic banyan-tree”. The stimulus is therefore in part conserved, held latent, and it comes out later.
Three orders have to be distinguished in what he demonstrates. The first is structural, there exists in the plant a conducting tissue that can be isolated, and that holds up, it is a dissection with an anatomy and measurements. The second is functional, the plant nerve and the animal nerve behave alike under ether, ammonia, tetanisation, and here everything rests on the resemblance in the shape of the curves. The third goes down to the psychic, memory brought back to a latent imprint that a diffuse stimulus reveals, on a tin wire as on a human retina, and that is what cost him most dearly. He never says that the plant thinks. He says that the mechanism is the same, and that the difference is one of degree.
The reception, for its part, teaches you something. On 6 June 1901, in London, Burdon Sanderson declares in session that the excitatory response of ordinary plants to mechanical stimulation is an impossibility, and Bose recalls the episode in his preface. The paper read that day would never be published. Ninety years later, an article in Nature establishes that a wounded tomato triggers its defences through an electrical signal, and not through chemical transport. Bose is knighted in 1917, elected to the Royal Society in 1920. The man was honoured long before his thesis was accepted.
The book ends on a sentence that states its whole programme: “the dividing frontiers between Physics, Physiology, and Psychology have disappeared”. What I took away from it lies in the gesture of chapter XXXII, crack the sheath, pull, and look at what comes out. The theory came afterwards.
Read in October 2016. Note written in 2026.
