General Physiology: An Outline of the Science of Life

The best method of employing galvanic stimulation with nonpolarisable electrodes upon a slide under the microscope, is to use a slide (Fig. 197) upon which two strips of porous clay, such as is used in the porous cups of the galvanic element, are cemented parallel to one another (a, a^) ; the ends of these strips are united by a wall of insulating cement (colophonium and wax) (b, Z^) ; thus a small open box is formed, in which can be placed a drop of water containing the objects to be investigated. The brushes of ordinary non-polarisable electrodes are laid upon the two parallel strips. It is possible by means of this small contrivance to send nearly parallel currents through the microscopic objects, and, at the same

FIG. 197. — Slide bearing a small box for the galvanic stimulation of microscopic objects, a, 01, Strips of fired clay ; b, bi, insulating walls of cement, which with the strips form a box, in which the objects are placed. time, to observe the effects of the stimulation under the microscope. If Actinosphcerium be stimulated by a constant current in this way, when it has protruded its pseudopodia from its spherical body, like the rays of the sun, it is found that, at the moment of making, phenomena of contraction may be observed in the pseudopodia that are extended in the direction of the anode and the kathode, the protoplasm coming together into small globules and spindles and streaming toward the body (Fig. 198). The pseudopodia that are extended perpendicularly to the direction of the current remain at rest. Hence, at the moment of closing there is both an anodic and a kathodic excitation of contraction. The excitation at the anode is the stronger of the two. Throughout the duration of the constant current the following is noticeable : At the kathode after the making, the phenomena of excitation gradually disappear, and the pseudopodia there assume their former smooth appearance, while upon the side of the anode the excitation

continues as long as the current remains. This latteris expressed in a constant advance of the phenomena of contraction. The protoplasm constantly draws back from the anode toward the body, and soon the pseudopodia are wholly drawn in. Then the contraction is noticed upon the body itself: the protoplasm of the walls of the vacuoles retracts more and more toward the interior, the vacuoles collapse, and the protoplasm itself disintegrates partly into its granules. This process of amalgamation and disintegration continues as long as the current flows, but gradually decreases in intensity. Hence there can be no doubt that the constant current stimulates throughout its duration. At the moment whenUhe

FIG. 198. — Actinosphcerium Eichhornii in four successive stages of polar excitation by the constant current. The protoplasm is disintegrating from the side of the anode. current is broken the amalgamation-process at the anode ceases at once. A few phenomena of stimulation are noticeable at the kathode, the pseudopodia again showing contraction-phenomena and their protoplasm flowing together into globules and spindles. But this effect gradually ceases and there is no complete retraction of the kathodic pseudopodia. If the current be not broken, the body of the Actinosphcerium disintegrates from the anode constantly, but in the course of time more slowly, until finally, if the current is feeble, the process wholly ceases. If, however, the current is stronger, the disintegration proceeds rapidly until the wrhole body has fallen into a lifeless mass of granules. Hence, Actinosphcerium is stimulated to contraction ly the making of the constant current at both the anode and the kathode, ly the breaking only at the kathode.

Exactly like Actinosphcerium, many marine rhizoppds, such as Orbitolites, Amphistegina (Fig. 199), and others, are stimulated by the making of the current to contract strongly at the anode and feebly at the kathode ; this phenomenon appears much more distinctly and purely in long, thread-like pseudopodia than in Actinosphcerium, since in the former the globules and spindles that are so thoroughly characteristic of all strong excitation of contraction develop at the two poles especially beautifully.1

In the ciliated epithelia of vertebrates Kraft ('90) saw likewise that upon passage of the constant current the ciliary motion was accelerated at both poles upon making. As regards the polar effect of the breaking he could not come to any definite conclusion. Finally, Loeb ('96, 4) has found very recently that in AmUystoma, an American urodele, the ~1~ cells of the cutaneous glands are stimulated at the anode by the making of the current so that a whitish secretion is extruded at that ' pole, in whatever direction the current is sent through the body.

Pelomyxa 2 behaves somewhat differently and also differently from muscle. If this lump of protoplasm be stimulated by a constant galvanic current, an excitation appears at the moment of making only at the anode, being expressed by a sudden, jerk-like contraction followed immediately by disintegration at the anodic side (Fig. 200). At the breaking of the current the same phenomenon occurs upon the kathodic side, while the disintegration at the anode immediately ceases. If, however, the current be kept made for a long time, the body disintegrates gradually from the anodic side into a dead mass. Hence, Pelomyxa shows likewise that the continued constant current acts as a continued stimulus. The irritability always becomes less, the longer the current remains made. If, after the action has continued for some time, the current

FIG. 199.— Amphistegina tessonii. (Cf. Fig. 170, p. 378.) The lenticular calcareous shell stands upon its sharp edge, and from the opening, which is directed toward the ground, sends in all directions thread-like pseudopodia ; upon these may be clearly recognised at the anode a very strong, and at the kathode a very feeble, excitation of contraction. be broken, the breaking frequently is no longer stimulating, and, in order to obtain a result on remaking, considerably stronger currents must be employed than before. The decrease of irritability under long action of the current is also the' reason why in Actinosphcerium, with the intensity of the current remaining equal, the amalgamation-process constantly decreases in intensity. Living substance loses in irritability under the long action of a stimulus. The law of excitation of Pelomyxa runs, therefore, as follows : Pelomyxa is stimulated to contraction at the anode upon making, and at the kathode upon breaking.

Another form of polar excitation, which is perhaps still more interesting, is shown by Amoeba proteus.1 If a constant current be sent through the body of the amoeba when the latter is extending its pseudopodia in various directions, it is seen that the body assumes at once the typical form of Amceba Umax, i.e., the extended form in which the protoplasm flows in a single direction, the body in a certain sense representing a single, large, thickpseudopodium.

FIG. 200. — Pelomyxa palustris. I, Normal, spherically contracted. //, At the moment of making, the protoplasm begins to disintegrate at the anode. It is thus shown that the extended body is stimulated to contraction at the anode, for here the characteristic vacuoles of Btitschli develop in the protoplasm, and the body retracts strongly upon this side. At the kathode, on the contrary, there exists an excitation of expansion, for here the protoplasm spreads out into a broad lobe. The phenomena are seen best when the direction of the current is, suddenly reversed, so that what was previously the anode now becomes the kathode, and vice versa (Fig. 201).

Wholly analogous relations have been demonstrated recently by Ludloff ('95) in Paramoecium. By the making of the current phenomena of contraction are shown in the external form of the body at the anode ; by strong currents that end of the body is compressed into a point, the liquid of the trichocysts is pressed out and, becoming coagulated in the form of threads, surrounds the end of the body with rays (Fig. 202, B). The polar excitation of the ciliary motion is much more characteristic. The cilia at the two

poles of the body are stimulated in opposite senses, the anodic to contract, their motion being stronger in the direction of the posterior end, and the kathodic to expand, the motion of these being stronger in the direction of the anterior end, in whatever relation to the direction of the current the body may be fixed (Fig. 202, C). Hence in Amoeba, as in Paramcecium, the making of the current produces at the two poles opposite effects, leading to contraction at the anode and to expansion at the kathode.

But, in reality, the polar effects of the galvanic current on muscle, as the later researches of Biedermann ('90, 1, 2) on smooth and cross-striated muscles have shown, are more complex than the law of excitation of muscle, in the form in which it has thus far been expressed, declares. The conception of excitation has hitherto been limited to the augmentation of these processes that in FIG. 201.— Amoeba proteus. At the lef t an unstimulated individual possessing numerous pseudopodia ; at the right two individuals stimulated by the galvanic current. At the anode a typical contraction is shown, at the kathode a strong expansion ; this is noticed especially clearly upon sudden reversal of the direction of the current.

contractile substances find their expression in contraction. Ex- pansion (relaxation) has customarily been regarded as a phenomenon of depression. This is incorrect. By depression is meant a diminution or complete cessation of the vital processes in question, as is exemplified by narcosis. Expansion, however, is based upon an augmentation of processes, just as is contraction. The confounding of expansion and depression leads to false ideas. The two conceptions should be sharply separated, and the term excitation should be extended to include the augmentation of those processes that in contractile substances find their expression in expansion. From Biedermann's researches it follows that the making of the constant current produces in the muscle not only an excitation of contraction at the kathode, but at the same time an excitation of expansion at the anode. In a muscle that is at the maximum of its extension the excitation at the anode can apparently not find

expression, for a muscle completely extended cannot be extended further. But that the process at the anode is as is stated above is seen at once when smooth or cross-striated muscles that are partially contracted are stimulated. In such muscles at the moment of making the current a local expansion takes place at the anode. Biedermann was likewise able to establish upon heart-muscle the FIG. 202. — Paramacium aurelia, polar excitation. A, Unstimulated individual. B, Action of a strong current ; the anodic end has become compressed into a point and the contents of the trichocysts have been extruded. C, The positions taken by the cilia (only the outline of the body is sketched) ; at the anode the cilia are bent more strongly toward the pointed hinder end of the body, at the kathode more toward the blunt forward end. D, The same, the position of the body being reversed. (After Ludloff.)

reverse fact, that upon breaking, in addition to the excitation of contraction at the anode, an excitation of expansion takes place at the kathode. It is interesting that the effects at the two poles upon making are the opposite of those upon breaking. The phenomena in the nerve afford a complete analogy to this. In the nerve also there are opposite effects at the two poles. This is expressed in the change in irritability that manifests itself at the poles when a galvanic current is passed through the nerve. For example,

experiments on the stimulation of nerves that are in the electrotonic condition have shown that upon the making of the current the irritability rises at the kathode in comparison with the normal, but at the anode is depressed ; this relation is completely reversed upon breaking, so that for a short time after breaking an increase of irritability at the anode and a decrease at the kathode are noticeable. Thus, opposite processes exist at the two poles upon

making, and each is reversed upon breaking. Whether similar relations between the effects of making and breaking on the one hand, and those of the two poles on the other, will be discovered in many free-living cells, later experiments must show. But that the opposition in the effects at the two poles upon making, which exist in muscle and nerve, is not to be generalised for all living substance, is shown by the simple fact that in Actinosphcerium, Or- Mtolites, and Amphistegina, it is not present ; in these forms an excitation of contraction alone appears at both the anode and the kathode.

In summarising briefly our knowledge of the polar effects of the galvanic current, it can only be said that the primary effects of the constant current are localised at the points of entrance into (anode) and exit from (kathode) the living substance ; in the different forms of living substance the kind of excitation at the kathode and at the anode upon making and upon breaking are very different ; hence, no general law of polar excitation, applicable to all living substance, can be formulated.

We will here leave the polar effects of the galvanic current and take up the various kinds of excitation-phenomena caused by electric stimulation. The effects upon contractile substances have already been considered to some extent. Contractile effects that are manifested outwardly in motion will now be examined. FIG. 203. — Tradescantia virginica. A cell from a stamen-hair. A, Unstimulated ; £, stimulated by an induction-current. The protoplasm has flowed together into globules and lumps at a,b,c,d. (After Ktthne.)

Expansion -effects of galvanic stimulation are mostly inconspicuous externally, and it has already been seen that only in certain cases is it possible to observe them at all. But contractioneffects are everywhere noticeable. Typical phenomena of contraction have already been seen in Actinosphcerium and Amphistegina in the formation of globules and spindles in the protoplasm of stimulated pseudopodia. Amoeba and leucocytes, as Golubew ('68) and Engelmann ('69) have shown, when acted upon by single inductionshocks, draw in their pseudopodia and assume a spherical shape. The protoplasm of plant-cells, as Klihne ('64) demonstrated in the cells of the stamen-hairs of Tradescantia virginica, is induced likewise to form globules by repeated making and breaking of the constant current or by single induction-shocks (Fig. 203) ; this is also characteristic of naked protoplasm, and can be produced locally by the local application of stimuli. The activity of cilia, as Engelmann (79, 1) and, more recently, Kraft ('90) have observed in ciliated epithelia, is increased to greater rapidity by the galvanic current, the frequency and amplitude of the stroke, and hence the useful effect, being especially influenced. In the single flagellum of the flagellate cell also, e.g., in Peranema, the exciting effect of the electric current can be observed expressing itself with a single induction-shock by an energetic stroke in the otherwise uniformly rhythmical beat (Fig. 204). In the myoids of Infusoria, e.g., in the stalk-myoid of Vorticella, in smooth musclecells, and in cross-striated muscle-fibres, excitation by a single, brief electrical stimulus, such as a single induction-shock, is expressed by a contraction ; with cross-striated skeletal muscles this can be recorded graphically by means of a myograph (Fig. 205).

But before bringing to an end the consideration of reactions in contractile substances, the effect of rapidly successive galvanic stimuli deserves attention. The best means of putting a contractile structure into tetanic contraction is afforded by the rhythmic induction-shocks of du Bois-Reymond's sledge-apparatus with the hammer in action. An amoeba or a leucocyte under the influence of rhythmically successive induction-shocks remains in contraction, i.e., preserves its spherical form, as long as the action continues. With the same kind of stimulus muscle likewise is in continual contraction. Muscle here affords a much more favourable opportunity than with mechanical stimulation to follow the origin of tetanus and to demonstrate the fact that tetanic contraction consists of discontinuous, single contractions, which follow

FIG. 204. — Peranema, a flagellate infusorian. a, Swimming quietly ; b, stimulated by an induction-shock. one another so rapidly that between them there is no time for the muscle to extend. In order to study the details of tetanic contraction, a myograph is employed (Fig. 206), the writing-lever of which traces the movement of the muscle upon stimulation in the form of a curve upon a revolving drum. If the muscle be stimulated by means of a single, not too strong induction-shock, so that it performs only a moderate contraction, a single curve is obtained, the ascending limb of which represents the phase of contraction, the descending limb the phase of expansion (Figs. 205, //, and 207, /). But, if several induction-shocks be allowed

FIG. '205. — /, Myograph. //, Curve of contraction. (After Helmholtz.) a, Moment of stimulation by an induction-shock. to act upon the muscle in succession and at regular intervals in such a manner that each succeeding stimulus reaches it at the moment when it is just beginning to extend, the first contractions are superposed, i.e., the shortening of the muscle is continued with every succeeding contraction ; the shortening of each contraction may be regarded as representing the resting point of the muscle, and from this the shortening of the next contraction rises. Thus, with every succeeding stimulus the curve of shortening rises like steps and reaches a certain height, at which it is then maintained, still allowing the regular variations

between the individual stimuli to be recognised clearly (Fig. 207, II). If induction-shocks be allowed to act upon the muscle in more rapid succession, as they are produced in the secondary coil by the play of Neef 's hammer, the effect of each single shock is no longer to be distinguished as such, but a smooth curve results, which rises rather steeply and then, if the stimulation be not continued too long, maintains itself at a uniform height as a straight line (Fig. 207, III). Thus, by increasing the rate of succession of the stimuli, it is possible to follow the formation of complete tetanus from the completely finished single contractions through all the transition-forms of incomplete tetanus, and thereby to afford the proof that, in reality, tetanus is a discontinuous cori-

FIG. 206. — Muscle-writer. The nerve-muscle preparation is fixed in the muscle-holder ; the nerve is stimulated by pointed platinum electrodes ; and the muscle records its movement upon a rotating, blackened drum by means of a writing-lever. traction. All continued contractions that are performed in the human body under nervous influence are, like tetanus artificially produced, discontinuous phenomena composed of many single contractions following one another in rapid succession.

It should be mentioned that there are forms of living substance that are not influenced at all by induction-shocks, either by single ones or by shocks succeeding one another rapidly or slowly, however strong they may be. Such objects are Orbitolites, Amphistegina, and other marine Rhizopoda. Their protoplasm requires for reaction a longer duration of the stimulus than the lightning-like induction-shock possesses.1 As regards other excitation-effects of galvanic stimulation, mechanical motile effects are produced, not only in contractile

substances, but in plants that, like Mimosa, move by changes of turgescence. If single induction-shocks be allowed to act upon FIG. 207. — Myographic curves from the gastrocnemius of the frog. 7, Single contractions produced by single opening induction-shocks. II, Incomplete tetanus, produced by opening in duction-shocks following in rapid succession. 777, Complete tetanus, produced by inductionshocks in very rapid succession. a Mimosa the branches and leaves of which are outspread, they have exactly the same effect as mechanical stimulation : the

branches drop at once and the leaves flap together in the typical manner. Other forms of energy are also made manifest by galvanic stimuli. Thus, exact thermo-electric measurements have shown that the temperature of muscle rises in activity, although very slightly, and that, in general, the production of heat stands in inverse proportion to the performance of work. That electricity is also produced in the contraction of muscle caused by galvanic stimulation is already clear from our previous knowledge ; an electric tension appears between every contracted point and every resting point, the former being negative to the latter. When, therefore, a contractionwave runs over the muscle from one end to the other, an action-current can be led off from the two ends at the moment when the wave begins, since, while the one end is contracting, the other is at rest.

Light also can be produced by galvanic stimulation in pelagic phosphorescent animals, such as Radiolaria and Noctilucce. It is evident from our previous considerations that all this evolution of energy in its various forms must be combined with an excitation of metabolism ; it is chiefly the much-investigated muscle that has shown this. The muscle excited to constant activity by stimulation of any sort consumes more oxygen than the resting muscle, it consumes the glycogen stored in it, it produces more carbonic acid than the resting muscle, and, in place of the neutral or alkaline reaction of the latter, it shows an acid reaction. All these changes show very clearly that in muscle when put into activity by stimuli a considerable augmentation of metabolism takes place.