General Physiology: An Outline of the Science of Life

But all cilia do not contract in one plane like those of the swimming-plates of the ctenophores. Many, especially certain flagella, describe more complicated paths, funnel-shaped, screwshaped, and like the path of a whip-lash, and accordingly the earlier physiologists distinguished several forms of ciliary movement. But whatever the path of vibration of the different cilia may be, the same principle lies at the basis of all, viz. : that a contractile side contracts from the cell-body outward, and thereby the opposite side is extended; in the phase of expansion the latter, by its elasticity, brings the cilium back into the position of rest. According to the relative positions of the contractile and the passively extended substances there results a movement in a plane or a more complicated form.

The work performed in ciliary movement is much less than that of muscular movement. Engelmann, Bowditch and others have calculated the work of ciliated epithelia, and recently Jensen {'93, 2) has measured the force of a single ciliate-infusorian cell, Paramcecium, which is well fitted for a great variety of investigations. Jensen determined that a Paramcecium, which possesses a length of about 0'25 mm., is able to raise a weight of 0*00158 mgr., i.e., about nine times the weight of its own body.

The view is sometimes expressed that amoeboid movement has nothing in common with muscular movement, and the latter nothing in common with ciliary movement, that the three are utterly different in kind. The above brief examination is sufficient to show, however, that these three forms of contraction constitute a, single group in contrast to all other modes of motion. It is true that they show among themselves certain differences, and that at first sight they appear quite unlike one another, but it has been seen that they all rest upon the same principle, namely, that of alternating diminution of surface (contraction) and increase of surface (expansion) by means of a rearrangement of the particles of the livingsubstance. That in amoeboid movement this shifting of the particles is wholly without rule, while in muscular and ciliary movements it is orderly, proves only that the two latter represent a higher stage of differentiation than the former. That, however, they stand in the closest genetic connection with amoeboid movement, that they have become evolved from it phylogenetically, is proved by numerous cases of transition, on the one hand between amoeboid and muscular movement, and on the other between amoeboid and ciliary movement. Engelmann ('81, 2) has found rhizopods (Acanthoeystis) possessing straight, filose, unbranched pseudopodia, which are capable of contracting longitudinally with excessive rapidity, and from which a small muscle-fibre is distin-

fuishable only by its constant differentiation: Engelmann has ttingly termed these pseudopodia myopodia. Moreover, man} cases have been observed where filose pseudopodia of amoeboid cells carry out pendular vibrations, at first irregularly and slowly, later rhythmically, until they have developed into genuine, constant cilia. In view of such facts no proof is needed to place beyond doubt the genetic connection of the three forms of contraction, even if careful observation of their single factors had not proved sufficiently clearly the identity of the principles upon

which they are based and their relationship in comparison with all other modes of motion. The contraction of living substance follows the same principle everywhere, whether the living substance creeps about as an Amaba upon decaying leaves in a pool of water, whether as a white blood-corpuscle it forces its way through lymph spaces in the tissues of the animal body, whether as a protoplasmic network it circulates in the cellulose-capsule of a plant-cell, whether as a muscle-fibre it performs the contractions of the untiring human heart, or, finally, as a cilium on the oviduct of woman it transports the unfertilised egg-cell to the uterus to undergo fertilisation,— everywhere there is the same phenomenon of alternating contraction and expansion of the living substance by means of the reciprocal rearrangement of its particles.

In the movements of living substance, especially in the phenomena of contraction, the transformation into kinetic energy of the potential energy introduced into the body as food, comes out very clearly. This is much less evident in the production of other forms of kinetic energy, such as light, heat, and electricity, for the demonstration of which very complicated methods and sensitive instruments are often required. Next to the mechanical energy of movement, the production of light is most evident to the senses, and has always had a mysterious fascination for the observer. It has a curious charm, when at night the water of a quiet sea breaks into a bright,, yellow glow at every stroke of an oar, or when in southern climates in the spring, the mild night air is filled by innumerable sparks, which silently flash up and circle about, and then disappear.

The emission of light by living substance is wide-spread. It is an especially significant fact that, of the wonderful pelagic animals whose delicate transparent bodies occupy the upper strata of the sea and float about as plankton, almost all possess luminous power. Associated with this fact is the presumption that the luminous capacity of living substance is possibly much widerspread than is realised, that we do not see the light because the organisms are not transparent, or because the production is too feeble to allow the light to be seen through thick body-layers; indeed, it is not impossible that in our own bodies certain cells may be photogenic. In most cases, as in luminous insects, the power of emitting light is a peculiarity specially perfected by selection and possesses its own significance for the life of the animals in question. In pelagic marine animals also such a significance is certainly present ; as a rule, these animals emit light

suddenly and only upon stimulation, and hence it may be supposed that the light serves as a means of frightening enemies (Fig. 112). The spontaneous emission of light is much less common. It appears especially in certain putrefactive bacteria that live upon decaying sea-fish and flesh (Bacterium phosphor escens), as well as in mushrooms (Agaricus), and certain insects (Mater, Lampyris). Numerous researches have been carried on respecting the nature of the light, e.g., those of Panceri and Secchi on Salpce (Pyrosoma), those of Moseley on deep-sea ccelenterates (Alcyonaria), and more recently, especially those of Langley and Very ('90) upon the lightning-bug (Pyrophorus noctilucus). To obtain a comparison

of insect-light and sunlight, Langley and Very superposed a spectrum of the light of Pyrophorus above the solar spectrum (Fig. 113), and thus determined that with equal luminosity the solar spectrum extends further toward both the violet and the red than the light of Pyrophorus, but that the latter is more intense than sunlight in the green. It is easily understood that the origin of so peculiar a phenomenon as organic luminosity has especially attracted the attention of investigators, and it is not surprising that an enormous literature upon the subject has appeared. Pfliiger (75, 1, 2) has collected a series of physiologically interesting accounts. It appears therefrom that very different views have been put forward upon the origin of the light in organisms. The idea early met with great approval, especially among non-specialists, that organic light depends upon the presence of phosphorus, to the mild light of which it has a certain external similarity. But exact investigations have shown that it has nothing whatever to do with phosphorus. This follows from the fact, among others, that the emission of light presupposes life in the cell. It can be observed in the single cell, a free-living bacterium from decaying fish, an infusorian or radiolarian from seawater, or a tissue-cell of a composite animal- or plant-body : but in every case the photogenic substance is produced only in

FIG. 112. — Noctiluca miliaris, a pelagic flagellated cell which becomes luminous upon stimulation. the cell-metabolism, although R. Dubois ('92) has shown that in certain animals, e.g., the boring mussel Pkolas, the substance can be extruded from the body as a cell-product without immediately losing its luminous power. Phosphorus is an active poison for all living substance ; hence, in the free state, in which it becomes luminous, it is wholly incompatible with the life of the cell. A trace of free phosphorus or luminous compounds of phosphorus has never been found in luminous animals. Nevertheless, it can be stated with certainty that the luminosity of living substance is associated, as in phosphorus, with very slow oxidation-processes. This follows especially from the fact that the light continues only in the presence of oxygen. Moreover, Fabre ('55) has found that the luminous mushroom, Agaricus, produces much more carbonic acid, when emitting light, than at other times. Finally, there belongs here a fact that was observed by

Max Schultze ('65) in the cells of the photogenic organs of lightning-bugs, namely, that these photogenic cells stand always in the 'closest connection with the tracheae, which serve as breathingtubes ; and, if they be placed under the microscope with perosmic acid, they withdraw oxygen from the latter, a fact which may be recognised by the appearance of a black precipitate. The photogenic cells, therefore, absorb oxygen actively. Pfliiger appropriately says concerning it : " Here, in the wonderful spectacle of animal phosphorescence nature has given us an example that shows where the taper burns that we call life." " It is certainly no rare exception, but only the special expression of the general law that all cells are burning continually, although with our corporeal eyes we do not see the light."

As regards the special processes of oxidation with which the luminosity of living organisms is associated, at present, with our very scanty knowledge of metabolism, almost nothing can be said with certainty. The beautiful researches of Radziszewski ('80) more than any others have elucidated this subject. Radziszewski studied in detail the conditions under which chemical substances exhibit phenomena of phosphorescence, and found that a whole series of organic bodies emit light when they are slowly combined with active oxygen in an alkaline solution. Such bodies comprise especially many fats, ethereal oils, hydrocarbons and alcohols. In many the light appears at ordinary temperatures, in others only upon warming. If, e.g., oleic acid be added to an alcoholic solution of potassium hydrate in a test-tube, a light lasting for a short time may be observed in the dark while the acid is being dissolved. If, after the light has ceased, a drop of a solution of peroxide of hydrogen be added to the liquid, a clear strip of light is seen to pass through the test-tube along with the drop of peroxide of hydrogen as it falls to the bottom. This is due to the fact that the peroxide of hydrogen gives off active oxygen to the oleic acid. The same phenomenon of light is shown still more clearly when oleic acid is dissolved in pure toluol, which likewise is capable of phosphorescence, and the solution is poured over a piece of potassium or sodium hydrate. The intensity of the light can always be increased by shaking, because the free atoms of oxygen are thus brought more into contact with the molecules of the phosphorescent body. If, e.g., into a glass bulb containing a mixture consisting of equal parts of pure toluol and cod-liver oil (which latter always contains in addition to oleic acid free atoms of oxygen), there be thrown a few pieces of potassium or sodium hydrate, and the whole be gently warmed and placed in the dark, no light is seen at first.

But, if the contents of the bulb be gently shaken, there is seen " at once a beautiful light streaming through the whole mass like a flash of lightning." It is in the highest degree probable that the luminosity of living substance depends upon analogous processes. Fats, oils, etc., are wide-spread in living substance, and Panceri believes of certain luminous marine fishes that the liquid fat is the luminous body. Substances that give an alkaline reaction are likewise found everywhere in living substance, and the luminosity of organisms is associated with processes of oxidation. Thus the same conditions are present in living substance as in the experiment of Radziszewski.

The production of heat is much less apparent to the senses than that of light. While we can observe the latter readily in the single cell, the amount of heat produced by the single cell, because of the small size of the object, cannot be measured with our crude instruments for the measurement of temperature. Nevertheless, it must be assumed that in the interior of every living cell heat is produced, for chemical processes are there present that are accompanied by the production of kinetic energy, and heat is the form of kinetic energy that is evolved in all such processes without exception, either alone or in addition to other forms of energy. In fact, there is even good ground for supposing with Pfliiger that in single molecules of living substance temperatures of several thousand degrees Centigrade become developed suddenly. This may be the case in the production of a molecule of carbonic acid, since the heat yielded by the combustion of carbon amounts to 8,000 calories. But the molecule of carbonic acid is excessively small, and it is surrounded in the cell by an enormous number of other molecules which possess a very low temperature. Hence, the heat that suddenly flashes up is counterbalanced as rapidly as it appears ; and, since all heat-forming molecules are not produced simultaneously, but appear now here and now there between large masses of other molecules, it is evident that the total temperature of the cell resulting from the equalisation of all the various individual temperatures cannot reach a remarkable height. Further, with our crude methods of heat-measurement, we cannot yet measure the actual heat given off to the outside by a single cell, since the greater part is lost in the process by conduction and radiation. It is, therefore, necessary to employ for the determination of the heat-production, not a single cell, but large cellcomplexes, such as considerable masses of tissue or whole organisms.

The production of heat is most evident in the bodies of homothermal, or so-called warm-blooded, animals. It has already been seen that the earlier division of animals into warm-blooded and cold-blooded has been very fittingly replaced by that into homothermal and poikilothermal animals, i.e., those that maintain under all external conditions the same body-temperature and those whose body-temperature rises and falls with the temperature of the environment. Homothermal animals show most clearly the production of body-heat because they have contrivances for storing up heat in themselves to a certain definite degree and maintaining it at this degree by an extremely delicate regulating mechanism. Hence, with an external temperature not too high the body of the homothermal animal is always warmer than the surrounding medium. This may be determined readily by the method of thermometric measurement. Thus, the body of man possesses in its interior a constant temperature of 37° — 39° C., upon its surface a temperature somewhat less, corresponding to the external cooling, in the mouth-cavity about 37° C., and in the axilla about 36'5° C. Birds with their active metabolism have the highest body-temperature, e.g., the swallow more than 44° C. But that poikilothermal animals can attain considerable temperatures when under conditions in which the heat produced by them is stored and

not given off to the medium by conduction or radiation, is proved by the fact that bees in their hives can produce temperatures of from 30° to 40° C. Even plants can raise their temperature above the temperature of the surroundings, as can be determined thermometrically, especially in sprouting and in vigorous growth where the metabolic processes are particularly active. Sachs was able to determine with a thermometer a rise of temperature of 1*5° C. in peas which were allowed to sprout in a funnel under a bell-jar (Fig. 114). Very remarkable temperatures have been observed in the spadices of the peculiar Aro'ideae during their development : here not rarely a rise of 15° C. is found. A rise which under favourable conditions can amount to more than 14° C. is produced also by yeast-cells in the fermentation of sugar solutions.

For the determination of delicate changes of temperature, especially in the tissues of poikilothermal animals, the rough method of measurement of temperature by the thermometer is not sufficient, and hence the finer method of thermo-electric measurement has been employed. As is well known, in a thermo-electric element, which consists of two pieces of different metals soldered together at one end (the best metals are German silver and iron, or antimony and bismuth), an electric tension is produced by slight warming of the soldered place. If the two free ends of the metals be joined by a wire so that a closed circuit exists, an electric current can be led off from them, the presence of which is shown by the deviation of a magnetic needle in the vicinity. For the demonstration of very feeble currents especially sensitive apparatus is needed, such as the multiplier and the galvanometer, the magnets of which are moved by very delicate currents. The multiplier consists of a suspended and easily moved astatic system, i.e., two horizontal magnetic needles which are fastened together parallel one above the other, so that the north pole of the one lies above the south pole of the other. In the region of the lower needle the wire of the circuit is wound into a coil consisting of an exceedingly large number of turns, so that when the current goes through it, all the individual turns tend to deviate the needle in the same direction. The upper needle hangs above a disc divided into degrees, so that here the deviation of the needle can be measured (Fig. 115). In the

FIG. 114. — Apparatus for demonstrating the rise of temperature in the sprouting of peas. Under a bell-jar is a funnel containing sprouting peas, into which projects a thermometer. e( After Sachs.) galvanometer (Fig. 116) the magnet has the form of a ring which is suspended by a silk fibre in the space within the coil ; a small mirror is connected with the ring and accompanies all the movements of the latter (Fig. 116 /3 7). At some distance from the apparatus stands a telescope bearing a scale, the image of which by careful adjustment can be observed through the telescope in the mirror of the galvanometer (Fig. 116 7). The slightest deviation of the ring-magnet is shown in the telescope by a shifting of the image of the scale. According to the extent of this shifting the strength of the electric current can be computed,

FIG. 115.— Multiplier. /, Plan. An astatic system, with the north poles N and N', is suspended upon a silk fibre G. Around the lower needle is a coil of wire W ; the upper needle moves above a graduated disc. (After Landois.) //, Multiplier complete. (After Cyon.) and hence empirically the amount of heating of the thermoelectric element, or, better, a whole series of thermo-electric elements. Thus the most delicate changes of temperature that a living tissue undergoes can be determined. By investigations of this kind it has been established that a higher temperature is produced by greater activity of the cells of a tissue, e.g., a gland or a muscle, than by less activity or during rest. This result is in close accord with our ideas concerning the production of heat, for the greater activity of the cells depends upon a greater metabolism in them, and heat results from chemical transformations in the cell. It is an old experience that one can warm himself by vigorous muscular activity.

All measurements of temperature, whether by the thermometer or the thermo-electric method, serve only to determine the temperature that prevails in some one place in the organism at some one time. They give no particulars regarding the quantity of heat that the organism or the individual tissue produces. But it is possible to determine the quantity of heat by investing the number of heat-units, or calories, that the living body gives off to the outside in a certain time. Thus calorimetry has developed by the side of thermometry. As is well known, a calorie is that

FIG. 116 a.— Mirror galvanometer. Upon a board is an upright, supported by two columns ; the upper portion consists of a glass tube in which hangs a silk fibre suspending a ring-magnet in the lower portion. At the two sides are two coils of wire. (After Cyon.) quantity of heat that is necessary to warm one kilogram of water from 0° C. to 1° C. In order to measure the number of calories that a living body, for example an animal, produces in a definite time, the water-calorimeter has been constructed (Fig. 117). This consists of a box having double walls that may be closed upon all sides. The space between the two walls is filled with water, the animal is placed in the box, and the whole is protected from cooling or warming from the outside by a non-conducting covering. The heat produced by the animal is communicated to the water

and raises its temperature ; the latter can be read off upon a thermometer projecting into the water. Various contrivances serve to reduce the sources of error that depend upon possible loss of heat. From the quantity of water and the warming of it in a FIG. 116/3. — A portion of the galvanometer enlarged. The two columns sustain a compartment within which is the ring-magnet in connection above with a small mirror ; the latter is suspended in a case (outlined in dotted lines) by the silk fibre, and accompanies all the movements of the magnet. (After Cyon.)

FIG. 116 y.— I. Arrangement of apparatus for thermo-electric measurement ; a, /, thermo-electric needles, which are joined together on one side by the wire b, and on the other by the wire 61 ; b is coiled about the ring-magnet m having the north pole n. The magnet mis suspended by a silk fibre c and fastened to a mirror s. In front of the ring-magnet is a straight magnet M, having the north pole N, at such a distance that the ring-magnet can still point toward the north. An extremely slight current suffices to cause it to deviate from its position. In front of the galvanometer is a telescope F with a scale KK, the image of which the observer B can see in the mirror s of the galvanometer ; thus he perceives every movement of the mirror or of the ring-magnet by the shifting of the image of the scale. II and III. Different forms of thermo-electric needles, a, German silver ; /, iron. (After Landois.)

definite time, the heat-production of the animal can be determined with approximate exactness. In recent times the watercalorimeter has been replaced by the air-calorimeter, in which the cage containing the animal is surrounded by a closed air-chamber ; the air of the chamber is expanded by the heat given off by the animal, and from the amount of the expansion the quantity of heat produced may readily be computed. Partly by one method and partly by another, Dulong, Desprez, Helmholtz, Rosenthal, and Kubner, have determined the quantity of heat produced by the animal body. Since all such heat is derived from the chemical energy of the food introduced into the body, and since all the energy of the body, in case the latter performs no work, is

FIG. 117. — Dulong's water-calorimeter. A box with double walls ; the wide space between the two walls contains water, through which a tube runs in spiral coils to the interior of the box for the admission of air from the outside at D to the animal, and for the removal of the used air through D'. At T and T" are thermometers. (After Rosenthal.) transformed finally into heat, the quantity of chemical energy that is introduced into the body with the food, expressed in calories, must according to the law of the conservation of energy be equal to the quantity of heat given off from the body to the outside. As a matter of fact, in the experiments this result has been attained with all desired exactness, and thus the validity of the law of the conservation of energy for the living body has been experimentally confirmed.

As with heat, so thus far the production of electricity cannot be proved upon the single cell, because even our most delicate apparatus is too gross. Here also masses of cells are required. But the production of electricity can be perceived without special means of aid in far fewer cases than the production of heat, since all homothermal animals show the latter. The former may be observed without further aid only where it occurs in large proportions, i.e., only in the electric fishes, whose powerful shocks were known even to the ancients. The history of the science of animal electricity is associated closely with the discovery of galvanism and with the names of Galvani and Volta. It is certainly a noteworthy fact that the discovery of the physical fact of galvanism required for its starting-point physiological phenomena.

In September, 1786, Aloisio Galvani was making investigations upon the terrace of his house in the ancient university city of Bologna on the influence of atmospheric electricity upon a frog's leg from which the skin had been removed. Several years before he had carried on similar researches with the aid of his wife, Lucia, since early deceased. In the course of his experiments he stuck a copper hook through the frog's spinal column, which was still in connection with the nerves. When he laid this preparation upon the iron railing of the terrace he noticed to his astonishment that whenever the hook touched the railing, the frog's leg attached to it executed violent contractions. This simple observation is said to have been the starting-point of the discovery of contact electricity, the inconceivable range of which in relation to civilisation is only now appreciated. Alessandro Volta discovered the explanation of this phenomenon by establishing the fact that in the contact of two different metals with a moist conductor an electric tension arises, which is equalised in the form of an electric current as soon as the metals are joined with one another. In Galvani's experiment the nerves and muscles of the frog constituted such a moist conductor between the copper hook and the iron railing ; the current went through the muscles and stimulated them so that they contracted. -This correct interpretation of Volta was opposed by Galvani, who imagined that the twitch of the frog's leg might be caused by electricity originating within the leg itself; but this error is said to have led him fortunately to a new discovery.

In labouring to prove to Volta that the contact of metals was not necessary for the production of the twitch, he endeavoured to bring out the twitch without metals ; and he succeeded in this by placing the free end of a freshly prepared nerve of a frog's leg in contact with the flesh. In this experiment, as is now known, the nerve is stimulated by the electric current produced in the muscle itself; and so Galvani became the discoverer of animal electricity, as previously, although unwittingly, he had discovered contact electricity.

Pfaff, Humboldt, Ritter, Nobili, Matteucci and others laboured in the further development of the science of animal electricity, but it was reserved for the classic investigations of du Bois- Reymond ('48 — '84) to place this field of physiology, which was then half-mystical and constituted one of the chief supports of the doctrine of vital force, upon a clear, exact foundation by creating for the first time sure and comprehensive methods of research. In the beginning, for evident reasons, only the muscles and nerves of the frog served as objects of experiment; but soon du Bois-Reymond brought into the range of his studies the interesting phenomena of the electrical fishes. And numerous inquirers, such as H. Munk, Hermann, Engelmann, Bernstein, and most recently Biedermann ('95), investigated the electrical phenomena of plants and various animal tissues. We are indebted to the researches of Hermann for the key to an understanding of the electrical

FIG. 118. — A, Simple arrangement for the production of a galvanic current. Zn, Zinc ; Cu, copper ; the two joined below by a moist thread. The arrows indicate the direction of the current. B, Simplest form of a galvanic element. Two metal strips (copper and zinc) dip into a liquid and are joined together by a metal at their free ends. The current goes in the direction of the arrow. phenomena of living substance. But it is due indisputably to the fundamental labours of du Bois-Reymond that the science of animal electricity has become one of the best-known branches of physiology.