General Physiology: An Outline of the Science of Life

that is carefully and slowly bathed with air containing the vapour of ether cannot be made to contract by any kind of stimulus. Nevertheless, the vital processes in the muscle are not at a complete standstill, as is evident from the fact shown by Biedermann ('85) that the narcotised muscle produces electricity when stimulated, just like the contracting muscle in the normal state. The stimulated part, as well as the artificial cross-section, appears by galvanometric investigation electrically negative to the resting part, as in normal conditions. In narcosis, therefore, certain metabolic processes must still remain

FIG. 168. Stentor coemleus. A, Wholly extended in rest; B, in the condition of moderate contraction as in free swimming ; C, completely contracted. undisturbed ; and perhaps this is true not only of muscle but of the narcotic conditions of all living substance. Recently, Massart ('93) has been able to abolish completely the development of light in Noctilucce by alcohol, by laying several sheets of filter-paper wet with alcohol over the vessel containing the seawater in which the organisms were swimming quietly upon the surface ; the vapours of the alcohol were thus forced into contact with the Noctilucce. After a short time the latter could not be induced by any stimulus to emit light.

Finally, best known are the depressing effects of narcotics upon the activity of the ganglion-cells of the central nervous system, both those that produce motor impulses, and those that are the seat of the sensations, of consciousness. In their anaesthetising action upon the cells of the central nervous system lies the extraordinary practical importance of the narcotics. Through the abolition of sensations, especially of pain, they confer enormous benefits upon mankind. But their misuse, especially that of alcohol and morphine, by inflicting irreparable injuries upon the

FIG. 169. — Ganglion-cells of a morphinised dog, stained by Golgi' most of the protoplasmic processes have assumed a monilifor s method. In A all, and in B :orm appearance. (After Demoor.) cells, produces most destructive effects and transforms the benefit into a serious evil. Recently a number of investigators, such as Meynert, Lepine, Duval, Solvay and others, have put forward the view that ganglion-cells possess the power of amoeboid motion, their protoplasmic processes, or dendrites, being able to shorten and lengthen. Hence it is highly interesting to show, as Demoor ('96) has very recently succeeded in doing, that under the influence of morphine in narcosis, and also of other stimuli, distinct phenomena of contraction can be observed in the dendrites of the ganglion-cells, or neurons, which correspond exactly to those contractile phenomena that

strong stimuli produce upon the branched pseudopodial filaments of Rhizopoda. The two pictures agree completely ( Cf. Fig. 169, A and jB). The dendrites of the neurons, for example in the brain of a dog, like the pseudopodia of the rhizopods, assume a very characteristic moniliform appearance in morphine- or chloralnarcosis, their protoplasm accumulating in numerous small globules and spindles. Evidently this phenomenon, which can be FIG. llO.—Ampkistegina lessonii. Filose pseudopodia project out through the opening of the lenticular, calcareous shell. At Normal ; £, in chloroform-narcosis.

produced only by an excitation of contraction, is an effect of the stage of excitation which the narcotics, as we have seen, cause in other forms of living substance before paralysis begins. In this condition the ganglion-cells are gradually paralysed, and during their narcosis preserve this form of pseudopodia. The same is readily observed1 also in the narcosis of Rhizopoda (Fig. 170), e.g., Amphistegina, Orbitolites, Rhizoplasma, etc. All changes in the pressure-relations of living substance in its environment may be termed mechanical stimuli. The effects of diminution of pressure have not thus far been investigated in detail, hence only the effects of increase of pressure are to be considered here.

Increase of pressure can take place in various ways, ranging from a light touch to a vigorous squeezing or complete crushing of the living substance, from a brief shock to a continuous and lasting pressure, or from an irregular shaking to rhythmically intermittent impacts, such as a tuning-fork produces. Among the excitationeffects of mechanical stimuli upon the phenomena of metabolism the clearest is that of the production of substance, secretion, in unicellular organisms. Actinosphcerium, e.g., when completely at rest, floats in the water, with many pseudopodia extended straight in all directions and evolving no secretion. Absence of secretion is evident from the fact that ciliate Infusoria belonging to the Hypotricha, which have cilia on their ventral side only and by means of them run over objects in the water like lice, not rarely walk along quietly upon the extended pseudopodia of the Actinosphcerium without sticking to them. But if one of the Hypotricha is actively swimming and bounds against a pseudopodium, the mechanical stimulus is sufficient to cause at the place of contact the secretion of a viscous substance, which holds fast the infusorian as prey.1 A single strong shock likewise causes the secretion of slime upon the pseudopodia, so that small particles suspended in the water remain sticking to them. Such secretion as the effect of mechanical stimulation is wide-spread in the naked protoplasmic bodies of Ehizopoda. The slime becomes directly visible in the large marine radiolarian Thalassicolla. It is possible with little trouble to extirpate from the round body of Thalassicolla, which has the size of a pea, the central capsule, which is pierced with extremely fine pores and contains protoplasm and nucleus. If this be done without injury to it, after a short time the capsule begins to regenerate into a complete radiolarian, i.e., to form new pseudopodia, and gelatinous and vacuolar layers (Cf. Fig. 171).

After the pseudopodia have become extended like a circlet of rays from the yellow spherical body, there is noticed between them an extremely delicate, very liquid slime, which is excreted by the pseudopodia and represents the rudiment of the new gelatinous layer. If in this stage the radiolarian be given a strong shock, it may be seen that the liquid mass of slime increases and becomes at the same time thicker and firmer ; this is manifested more distinctly when the shock is repeated.1 The mechanical stimulation promotes visibly the secretion of slime.

No excitation-effects of mechanical stimulation upon the phenomena of form-changes, upon growth and cell-division, are thus far known. Effects of excitation upon the phenomena of the transformation of energy have been investigated very fully, and a great FIG. 171. — Thalassicolla nucleata, a spherical radiolarian cell. A, Uninjured individual in optical section. In the middle lies the central capsule, containing the nucleus, surrounded by black pigment. B, Central capsule removed. It has already surrounded itself with a new" circlet of pseudopodia. C, The same central capsule after strong stimulation. The pseudopodia are somewhat drawn in, and between them a thick mass of slime has been secreted. B and C strongly magnified.

mass of observed facts exists. From these we will select the typical phenomena. Those connected with motion, which are called out by mechanical stimuli, constitute here also the chief point of interest. The production of turgescence-movements in the so-called sensitive plants, such as the delicate Mimosa pudica, is generally known. Mimosa, which resembles a small Acacia tree, during the day and while undisturbed holds its primary petioles, which spring from the trunk, directed obliquely upward. The secondary petioles, which bear the rows of leaflets, are spread out wide apart, and the leaflets themselves stand horizontal and widely extended (Fig. 172, A). But as soon as the pot in which the plant is growing is shaken, the picture changes almost immediately. The primary petioles fall down as a result of the decrease of the turgor of the cells of their pulvini, the secondary petioles turn toward each other, while the leaflets are raised and lie with their upper surfaces together (Fig. 172, B). The plant, when left at rest, remains for some time in this position , and then very gradually returns to its original condition, the cellturgor again increasing at the corresponding portions of the pulvini. In the single leaflet the position of stimulation can be called out

FIG. 172. — Mimosa pudica. A, A branch uiistimulated and extended ; £, a branch stimulated and fallen, with its leaves folded. (After Detmer.) also by a very gentle local touch. If the touch be stronger, the leaflets may be seen to move in succession like a row of dominoes, thus affording a very striking demonstration of the transmission of the stimulus. Among the contraction-movements resulting from the mechanical stimuli the contraction-phase only is thus far recognised with certainty, although it is not improbable that in many cases very delicate tactile stimuli may produce expansion. Thus, the contact of an amoeboid protoplasmic mass with a smooth support might influence by cohesion the extension of the pseudopodia.

In the naked protoplasmic bodies of Rhizopoda a single shock upon the extended pseudopodia, such as can be produced by a vigorous rap of the slide under the microscope, produces more or less pronounced phenomena of contraction, according to the very various grades of irritability of the different species.1 An Amceba or an Adinosphcerium, stimulated in this way, ceases momentarily its centrifugal protoplasmic streaming, i.e., the extension of its pseudopodia; upon stronger stimulation there may be a partial indrawing of the pseudopodia, a transitory centripetal streaming. Other forms, such as Difflugia, react more energetically (Fig. 173). With a gentle shock the pseudopodia become slowly more or less retracted, their previously smooth contour becoming wrinkled

FIG. ns.—Difflugia. From the shell of sand-grains project three finger-like pseudopodia. A, Unstimulated ; B, stimulated by a gentle shock. (Fig. 173, B ) ; with a stronger shock the pseudopodia are frequently drawn with such force into the protoplasmic body, that their ends, being fastened to the support by means of a sticky secretion, are torn off. With stronger stimulation the change in the pseudopodia is much more pronounced than with feebler : they become not only wrinkled, but on their whole surface small droplets swell out from the smooth contour ; 2 the more the reaction develops, the larger become the droplets ; they flow together into n myelin-like mass, and are distinguished clearly by a strongly refractive strand visible in the axis of the pseudopodium (Fig. 174) ; 1 Of. Verworn ('89, 1). 2 C£ Fig. 156) p> 363-

finally, the latter is wholly drawn in, and its mass mingles with the rest of the body-protoplasm. Among the marine PolytJialamia also there are many forms that possess very great irritability ; these draw FIG. 174.— Contraction of a pseudopodium of Diffliiffia lobostoma after vigorous shaking Seven successive stages of retraction. in their whole richly-branched network of pseudopodia upon a single j shock. In the same manner there can be observed upon the slide under the microscope the effects of a shock upon the motion of flagella and cilia. E.g., Peranema, by means of the regular lashings of the flagellum at its anterior end, moves through the water quietly and in a straight line (Fig. 175). But, if the slide be given a brief shock, there follows at once an energetic lashing of the whole flagellum, which gives the cell another direction. It then continues its way quietly as before, with only the end of its flagellum vibrating. The mechanical stimulus, therefore, has had the result of intensifying the stroke of the flagellum. The same thing can be observed in the ciliary motion of the ciliate Infusoria. If a Paramcecium be observed in quiet and not too rapid locomotion, moving through the water by the play of its cilia as by innumerable small and rapidly moving oars, it is seen that upon being jarred it suddenly accelerates its motion, returning immediately, however, Fl<?- ITS.— Pemnema, a

tO its preVlOUS rate. IhlS tact may be a, Swimming quietly; b, which usually lies in the water for a long time absolutely still and keeps its long, ray-like cilia completely quiet (Fig. 176). At the moment when it is slightly shaken, it suddenly makes a few, very energetic strokes with its cilia, so that it springs through the water like a flea, and immediately thereafter becomes quiet in another spot. Similar cases exist in great abundance among the active Infusoria. It is found everywhere that mechanical stimuli cause energetic strokes of cilia.

Infusorian life offers innumerable opportunities to observe the effects of mechanical stimuli upon muscular motion. Smooth muscle-fibres (rnyoids) are wide-spread among Infusoria ; and just as everything in the life of these Protista, which are in endless activity, takes place with great rapidity, so their contractile fibres react upon the slightest jarring with a sudden, strong contraction. There are few sights in the microscopic world so pleasing as the

FIG. 176. — Pleuronema chrysalis. A, Lying still. E, In the act of springing, upon being stimulated by shaking ; the cilia are just performing a stroke. contraction of a much-branched tree of Vorticellince upon very slight jarring (Fig. 177). At the moment of the impulse all the stalkmyoids contract suddenly and simultaneously, and the stalks are coiled in delicate spirals (Fig. 177, B). Stentor also, which in rest has its beautiful, trumpet-shaped body unfolded, at every jar suddenly draws itself into a stalked ball by the contraction of the many myoid-fibres lying in the external layer of the body (Fig. 168, p. 376). The cross-striated muscles of the higher animals behave similarly, without of course possessing the same high grade of irritability. In order to cause contraction, by means of a mechanical stimulus, in a frog's muscle, for example, a stronger shock to the muscle-substance is needed than in the case of an infusorian.

Every one who has been at the sea-shore upon a quiet summer evening has observed the production of light by mechanical stimuli. The curious, transparent animal life that in quiet weather exists at the surface of the water has the wonderful power, irrespective of the classes to which the animals severally belong, of glowing brilliantly at every movement of the boat or the oars, or every dash of the waves. Where the water contains much plankton, such as Noctihwce, Radiolaria, eggs of Ctenophora, etc., the effect of a shower of sparks in the water can be produced as well indoors. Every time sea-water is stirred in a glass the unicellular organisms, at the moment of the touch with a glass rod, flash up brightly, and then immediately sink again into

FIG. 177. — Carchesium polypinum, a branched colony of Vorticellince. A, Unstimulated ; B, stimulated by jarring. The single individuals jerk together by the contraction of the-myoids of their stalks. darkness. The experiment can be repeated innumerable times, and the spectacle that is presented is of wondrous beauty. Before leaving the excitation-effects of mechanical stimuli, one more group deserves attention, viz., the results of rhythmically repeated shocks. Phenomena that are produced only incompletely by single shocks are expressed much more strongly by summation, providing that each succeeding impulse follows before the stimulus of the preceding one has passed away. This fact is demonstrated most distinctly in contraction-movements, where one contraction is superimposed upon another so that there is no time for expansion to develop between them ; a genuine cramp then appears, which is termed mechanical tetanus. The peculiarity of tetanus lies in the fact that, although composed of many single contractions, on account of their rapid succession it gives the impression of a continual process. The simplest method of producing rhythmic shocks is either to shake the objects in a shallow basin by means of a rotating toothed wheel that has wide

teeth, or to fasten them upon a thin glass slide upon one limb of a tuning fork of the proper pitch and draw a violin bow across the other limb. Observation immediately after the experiment shows that Amoeba, Actinosphcerium, and other rhizopods have drawn in FIG. 178. — Amoeba. A, Normal ; B, after tetanic stimulation upon a tuning fork. their pseudopodia completely and are in the stage of complete contraction, i.e., more or less completely spherical (Fig. 178). If the experiment be interrupted after a brief period of shaking, according to the time of the interruption the various stages in the formation of tetanus can be observed. The pseudopodia are then

FIG. 179 — Actinosphcerium. A, Undisturbed ; B, at the beginning of strong tetanic stimulation ; C, in complete mechanical tetanus. incompletely retracted. The phenomena in long, thread-like pseudopodia, such as in Actinosphcerium or Orbitolites, are characteristic (Figs. 179 and 180). With very slight shaking the pseudopodia remain smooth and straight, as they were when undisturbed, and their protoplasm flows slowly but constantly without exception in a centripetal direction. But, if the shaking be more intense, they assume a varicose appearance, their centripetally streaming protoplasm collecting into many small spindles and globules, of which the smaller flow into the adjacent larger ones, while the larger ones constantly approach the central protoplasmic body; upon long-continued action all protoplasm flows into the cell-body.1 This curious formation of droplets upon pseudopodia is a peculiarity of strongly and continually stimulated protoplasm which is general in Rhizopoda that are provided with filose pseudopodia ; it is only a special case of the general law that strong stimuli cause naked protoplasmic masses

FIG. 180.— Orbitolites. A part of the surface of the shell, with extended, thread-like pseudopodia. A, Unstimulated ; B, after vigorous shaking. to assume the spherical form. The same tendency toward the formation of globules, which all stimulated protoplasm as a whole shows, is also noticeable in its individual parts.2 Ciliary motion is increased greatly by rhythmically intermittent shocks, so that Infusoria stimulated in this way rush madly through the water for a considerable time after the stimulation has ceased. A real tetanus, however, in which the cilia remain bent in the position of contraction, appears not to occur, at least thus far such has not been observed. The rhythmic motion of the cilia continues, and is changed in its rate and amplitude only.

On the other hand, in the muscle mechanical tetanus can be produced very easily. Vorticella, stimulated in the above-described manner, passes at once into tetanus. The stalk-muscle remains continually contracted. The tetanus is frequently so great that the cell -bodies are loosened from their stalks and swim away. A short time after the cessation of the stimulation the isolated stalks extend again, but rarely continue to live for any length of time. Cross-striated muscle can likewise be put into tetanus by a hammer acting rhythmically and arranged to strike carefully upon the muscle ; the latter remains contracted throughout the duration of the stimulus.

One might easily be misled by external appearances into regarding the tetanus of contractile substances as a phenomenon of depression, for Amoeba, Actinosphcerium, muscle, etc., during the tetanic condition are apparently in complete rest and motionless, like the same objects when a narcotic has acted upon them. But the two conditions have absolutely nothing to do with one another. The difference is fundamental, as is shown by an investigation of the metabolism. While in narcosis the metabolism undergoes a real depression, researches have shown that in tetanised muscle the metabolism is considerably increased. The decomposition-products of the living substance, such as carbonic acid, lactic acid, etc., undergo an extraordinary increase in quantity ; certain substances that have accumulated in the muscle, such as glycogen, become consumed ; and the production of heat becomes increased to a considerable degree. It follows from this that in the tetanic condition the vital process experiences a considerable augmentation, that tetanus is a phenomenon not of depression but really of excitation.

The production of light by Noctiluca upon intermittent stimulation appears to be a continual process analogous to the tetanus of contractile substances. After a short time this phenomenon decreases very considerably in intensity.1 The phenomena of depression that are called out by mechanical stimuli are as rare as the exciting effects of such stimuli are manifold and wide-spread, and they have been little investigated. Horvath ("78), and later in agreement with him Reinke ('80), made the statement that the growth of Bacteria the cultures of which are continually exposed to regular shocks, is interfered with, in other words a depression of groAvth takes place. Later the validity of these experiments was called in question by others; but recently Meltzer ('94), in a detailed series of

experiments, confirmed in essential the observations of Horvath and Reinke by showing that regular vibrations are able to produce not only an inhibition of growth, but under certain conditions even complete death and granular disintegration of the protoplasm. Further, Engelmann (79, 1) made the observation that the motion of Diatomece and Oscillarice ceases upon shaking. But here the question is undecided whether the standstill is to be interpreted as a phenomenon of depression or the expression of tetanic excitation, like the cessation of protoplasmic motion in tetanised Amoebae.

Finally, in the pressure-paralysis of nerves we have, at all events, a real phenomenon of depression which is to be classed with those produced by narcotics. This pressure-paralysis, which appears when a nerve is compressed for a time but not too strongly, is generally known as the " feeling of going to sleep " of the limbs. Besides the subjective phenomena, the " going to sleep " expresses itself in a diminution or complete interruption of the power of conductivity of the compressed nerve, so that for some time the muscles supplied by the latter cannot be stimulated through it to contraction. A short time after the cessation of the pressure the power of conduction is again established.

This comprises approximately all the facts known regarding depressing effects of mechanical stimuli. The employment of thermal stimulation allows far fewer variations to be made than that of mechanical or even chemical stimulation, for only a rise or a fall of temperature can act as a stimulus upon living substance. In accordance with the nature of the thermal stimulus rapid rhythmical variations of temperature cannot be produced, since heat requires a long time to be communicated to a body or to disappear from it. Hence it is impossible to produce a thermal tetanus corresponding to mechanical tetanus. Thermal stimulation is thus very simple, and its effects are likewise simply shown.

Starting from the average temperature at which a cell normally exists, which, therefore, represents the optimum of the vital condition, it is found to be a general law that up to a certain point excitation increases with increasing temperature. This holds good for very different vital phenomena and for very different forms of living substance. The best example of the excitation of metabolism by increasing temperature is afforded by the activity of yeast-cells, since in the quantity of carbonic acid that is derived from the decomposition of grape-sugar there is given an excellent measure of the increase of metabolism. . The evolution of carbonic acid in a solution of grapesugar containing yeast is always more active with increasing temperature up to about 30° — 35° C., when it becomes very violent.1 The bubbles of carbonic acid rise in the fermentationtube as in sparkling champagne. Plant-life likewise affords many clear examples of how with rising temperature within certain limits the vital phenomena, such as cleavage Jof carbonic acid, formation of starch, of proteid, etc., increase in intensity ; it is here found that the temperatures at which the excitation reaches its maximum are very different, not only for the different forms of living substance, but also for the various metabolic processes in the same object. It is observed also in animals that metabolism increases proportionally with the temperature; and Spallanzani showed for cold-blooded animals, especially for snails, that the consumption of oxygen is thus increased. Whatever may be the details of the metabolism, the law holds good everywhere in the living world, that the intensity of metabolism increases with increasing temperature.

It should be mentioned, however, that there is, apparently, an exception to this general law. This is shown by the behaviour of homothermal (warm-blooded) animals. It is a well-known fact that warm-blooded animals undergo a decrease of metabolism with rising temperature. Man in winter has a much more active metabolism than in summer, he consumes most food at the lowest, least at the highest degrees of temperature. Thus far this remarkable paradox has been little explained, and Pfliiger (78), who has studied the subject in detail, arrives at a solution of the apparent contradiction only by the aid of certain hypotheses. As is well known, the peculiarity of warm-blooded animals in contrast to all others is the possession of a mechanism in their nervous system that regulates reflexly the temperature of the body and maintains it at a constant height, however great variations the external temperature may undergo. The metabolism, which is the source of heat-production in the animal organism, is, however, in the warm-blooded animals, the servant of the heat-regulating mechanism. If the external temperature is low, the metabolism and with it the production of heat are increased reflexly through the nervous system from the skin, in order to compensate for the^ greater loss of heat by the body ; and, vice versa, if the external temperature is high, the metabolism and with it the production of heat undergo, likewise reflexly, a corresponding depression. The increase of metabolism of the cells in cold and the decrease in 1 Cf. von Liebig (70).