Response in the Living and Non-Living.
by Jagadis Chunder Bose.
PREFACE
I have in the present work put in a connected and a more complete form results, some of which have been published in the following Papers:
"De la Generalite des Phenomenes Moleculaires produits par l"Electricite sur la matiere Inorganique et sur la matiere Vivante." (_Travaux du Congres International de Physique._ Paris, 1900.)
"On the Similarity of Effect of Electrical Stimulus on Inorganic and Living Substances." (_Report, Bradford Meeting British a.s.sociation, 1900.--Electrician._)
"Response of Inorganic Matter to Stimulus." (Friday Evening Discourse, Royal Inst.i.tution, May 1901.)
"On Electric Response of Inorganic Substances. Preliminary Notice."
(Royal Society, June 1901.)
"On Electric Response of Ordinary Plants under Mechanical Stimulus."
(_Journal Linnean Society_, 1902.)
"Sur la Reponse Electrique dans les Metaux, les Tissus Animaux et Vegetaux." (Societe de Physique, Paris, 1902.)
"On the Electro-Motive Wave accompanying Mechanical Disturbance in Metals in contact with Electrolyte." (_Proceedings Royal Society_, vol. 70.)
"On the Strain Theory of Vision and of Photographic Action." (_Journal Royal Photographic Society_, vol. xxvi.)
These investigations were commenced in India, and I take this opportunity to express my grateful acknowledgments to the Managers of the Royal Inst.i.tution, for the facilities offered me to complete them at the Davy-Faraday Laboratory.
J. C. BOSE.
DAVY-FARADAY LABORATORY, ROYAL INSt.i.tUTION, LONDON: _May 1902._
CHAPTER I
THE MECHANICAL RESPONSE OF LIVING SUBSTANCES
Mechanical response--Different kinds of stimuli--Myograph--Characteristics of response-curve: period, amplitude, form--Modification of response-curves.
One of the most striking effects of external disturbance on certain types of living substance is a visible change of form. Thus, a piece of muscle when pinched contracts. The external disturbance which produced this change is called the stimulus. The body which is thus capable of responding is said to be irritable or excitable. A stimulus thus produces a state of excitability which may sometimes be expressed by change of form.
#Mechanical response to different kinds of stimuli.#--This reaction under stimulus is seen even in the lowest organisms; in some of the amoeboid rhizopods, for instance. These lumpy protoplasmic bodies, usually elongated while creeping, if mechanically jarred, contract into a spherical form. If, instead of mechanical disturbance, we apply salt solution, they again contract, in the same way as before. Similar effects are produced by sudden illumination, or by rise of temperature, or by electric shock. A living substance may thus be put into an excitatory state by either mechanical, chemical, thermal, electrical, or light stimulus. Not only does the point stimulated show the effect of stimulus, but that effect may sometimes be conducted even to a considerable distance. This power of conducting stimulus, though common to all living substances, is present in very different degrees. While in some forms of animal tissue irritation spreads, at a very slow rate, only to points in close neighbourhood, in other forms, as for example in nerves, conduction is very rapid and reaches far.
The visible mode of response by change of form may perhaps be best studied in a piece of muscle. When this is pinched, or an electrical shock is sent through it, it becomes shorter and broader. A responsive twitch is thus produced. The excitatory state then disappears, and the muscle is seen to relax into its normal form.
#Mechanical lever recorder.#--In the case of contraction of muscle, the effect is very quick, the twitch takes place in too short a time for detailed observation by ordinary means. A myographic apparatus is therefore used, by means of which the changes in the muscle are self-recorded. Thus we obtain a history of its change and recovery from the change. The muscle is connected to one end of a writing lever. When the muscle contracts, the tracing point is pulled up in one direction, say to the right. The extent of this pull depends on the amount of contraction. A band of paper or a revolving drum-surface moves at a uniform speed at right angles to the direction of motion of the writing lever. When the muscle recovers from the stimulus, it relaxes into its original form, and the writing point traces the recovery as it moves now to the left, regaining its first position. A curve is thus described, the rising portion of which is due to contraction, and the falling portion to relaxation or recovery. The ordinate of the curve represents the intensity of response, and the abscissa the time (fig. 1).
[Ill.u.s.tration: FIG. 1.--MECHANICAL LEVER RECORDER The muscle M with the attached bone is securely held at one end, the other end being connected with the writing lever. Under the action of stimulus the contracting muscle pulls the lever and moves the tracing point to the right over the travelling recording surface P.
When the muscle recovers from contraction, the tracing point returns to its original position. See on P the record of muscle curve.]
#Characteristics of the response-curve: (1) Period, (2) Amplitude, (3) Form.#--Just as a wave of sound is characterised by its (1) period, (2) amplitude, and (3) form, so may these response-curves be distinguished from each other. As regards the period, there is an enormous variation, corresponding to the functional activity of the muscle. For instance, in tortoise it may be as high as a second, whereas in the wing-muscles of many insects it is as small as 1/300 part of a second. "It is probable that a continuous graduated scale might, as suggested by Hermann, be drawn up in the animal kingdom, from the excessively rapid contraction of insects to those of tortoises and hibernating dormice."[1]
Differences in form and amplitude of curve are well ill.u.s.trated by various muscles of the tortoise. The curve for the muscle of the neck, used for rapid withdrawal of the head on approach of danger, is quite different from that of the pectoral muscle of the same animal, used for its sluggish movements.
Again, progressive changes in the same muscle are well seen in the modifications of form which consecutive muscle-curves gradually undergo.
In a dying muscle, for example, the amplitude of succeeding curves is continuously diminished, and the curves themselves are elongated.
Numerous ill.u.s.trations will be seen later, of the effect, in changing the form of the curve, of the increased excitation or depression produced by various agencies.
Thus these response records give us a means of studying the effect of stimulus, and the modification of response, under varying external conditions, advantage being taken of the mechanical contraction produced in the tissue by the stimulus. But there are other kinds of tissue where the excitation produced by stimulus is not exhibited in a visible form.
In order to study these we have to use an altogether independent method, the method of electric response.
FOOTNOTES:
[1] Biedermann, _Electro-physiology_, p. 59.
CHAPTER II
ELECTRIC RESPONSE
Conditions for obtaining electric response--Method of injury--Current of injury--Injured end, cuproid: uninjured, zincoid--Current of response in nerve from more excited to less excited--Difficulties of present nomenclature--Electric recorder--Two types of response, positive and negative--Universal applicability of electric mode of response--Electric response a measure of physiological activity--Electric response in plants.
Unlike muscle, a length of nerve, when mechanically or electrically excited, does not undergo any visible change. That it is thrown into an excitatory state, and that it conducts the excitatory disturbance, is shown however by the contraction produced in an attached piece of muscle, which serves as an indicator.
But the excitatory effect produced in the nerve by stimulus can also be detected by an electrical method. If an isolated piece of nerve be taken and two contacts be made on its surface by means of non-polarisable electrodes at A and B, connection being made with a galvanometer, no current will be observed, as both A and B are in the same physico-chemical condition. The two points, that is to say, are iso-electric.
If now the nerve be excited by stimulus, similar disturbances will be evoked at both A and B. If, further, these disturbances, reaching A and B almost simultaneously, cause any electrical change, then, similar changes taking place at both points, and there being thus no relative difference between the two, the galvanometer will still indicate no current. This null-effect is due to the balancing action of B as against A. (See fig. 2, _a_.)
#Conditions for obtaining electric response.#--If then we wish to detect the response by means of the galvanometer, one means of doing so will lie in the abolition of this balance, which may be accomplished by making one of the two points, say B, more or less permanently irresponsive. In that case, stimulus will cause greater electrical disturbance at the more responsive point, say A, and this will be shown by the galvanometer as a current of response. To make B less responsive we may injure it by means of a cross-sectional cut, a burn, or the action of strong chemical reagents.
[Ill.u.s.tration: FIG. 2.--ELECTRIC METHOD OF DETECTING NERVE RESPONSE (_a_) Iso-electric contacts; no current in the galvanometer.
(_b_) The end B injured; current of injury from B to A: stimulation gives rise to an action current from A to B.
(_c_) Non-polarisable electrode.]
#Current of injury.#--We shall revert to the subject of electric response; meanwhile it is necessary to say a few words regarding the electric disturbance caused by the injury itself. Since the physico-chemical conditions of the uninjured A and the injured B are now no longer the same, it follows that their electric conditions have also become different. They are no longer iso-electric. There is thus a more or less permanent or resting difference of electric potential between them. A current--the current of injury--is found to flow _in the nerve_, from the injured to the uninjured, and in the galvanometer, through the electrolytic contacts from the uninjured to the injured. As long as there is no further disturbance this current of injury remains approximately constant, and is therefore sometimes known as "the current of rest" (fig. 2, _b_).
A piece of living tissue, unequally injured at the two ends, is thus seen to act like a voltaic element, comparable to a copper and zinc couple. As some confusion has arisen, on the question of whether the injured end is like the zinc or copper in such a combination, it will perhaps be well to enter upon this subject in detail.
If we take two rods, of zinc and copper respectively, in metallic contact, and further, if the points A and B are connected by a strip of cloth _s_ moistened with salt solution, it will be seen that we have a complete voltaic element. A current will now flow from B to A in the metal (fig. 3, _a_) and from A to B through the electrolyte _s_. Or instead of connecting A and B by a single strip of cloth _s_, we may connect them by two strips _s s"_, leading to non-polarisable electrodes E E". The current will then be found just the same as before, i.e. from B to A in the metallic part, and from A through _s s"_ to B, the wire W being interposed, as it were, in the electrolytic part of the circuit.
If now a galvanometer be interposed at O, the current will flow from B to A through the galvanometer, i.e. from right to left. But if we interpose the galvanometer in the electrolytic part of the circuit, that is to say, at W, the same current will appear to flow in the opposite direction. In fig. 3, _c_, the galvanometer is so interposed, and in this case it is to be noticed that when the current in the galvanometer flows from left to right, the metal connected to the left is zinc.
Compare fig. 3, _d_, where A B is a piece of nerve of which the B end is injured. The current in the galvanometer through the non-polarisable electrode is from left to right. The uninjured end is therefore comparable to the zinc in a voltaic cell (is zincoid), the injured being copper-like or cuproid.[2]