« VorigeDoorgaan »
and, in fact, nearly all that is now written
This may be considered as the first part of the experiments. The second part is even more interesting, as it disclosed further analogies between electro-magnetism and light. Light is transmitted by some bodies, and is reflected by other bodies. Electro-magnetic waves behave in the same way; a plate of zinc acts upon them as a mirror and sends them back, but they pass through a wooden door just as light passes through a window plate. Hertz could send them into the next room through a shut door. If we put a red-hot iron ball in the focus of a parabolic mirror, we may make it light a match adjusted in the focus of another parabolic mirror which is placed at the other end of a room. Electricity behaves in the same way; we can send beams of electrical oscillations by means of a parabolic mirror, and intercept them at a distance by another mirror and send them into its focus. If we in terrupt the initial discharges in a certain way-as they are interrupted in the Morse alphabet - we shall transmit electrical signals and have a telegraph without connecting wires. Light is refracted by transparent bodies if they have the shape of a prism or a lens; and by means of a big prism of pitch Hertz refracted the Another important matter was to study electro-magnetic "rays;" he could bend the magnetic part of the same electric disthem, and send them under a right angle turbances. In Maxwell's theory the maginto another room. Reflected light can be netic disturbances ought to be nothing polarized, and electro-magnetic "rays "but transversal rotations of the particles are polarized, too. In short, Maxwell's hypothesis as to the identity of light and electricity is fully confirmed. Both are disturbances (vibrations, or whatever they might be) in the usual state of ether which are transmitted like all other kinds of energy-like the energy of the billiard ball, the stone, and the tuning-fork, of which we spoke at the beginning of this chapter, that is, from one particle to the
So we finally part with the mysterious "electric fluid "just as we parted, thirty years ago, with the "caloric fluid," and we simply have before us a separate mode of energy. When the waves of ether have lengths of from '000012 to 000016 parts of an inch, we have chemical energy; when they follow each other at distances of from 000016 to 00003 parts of the inch, our eye sees them as light; when they grew to 00012 parts of the inch, we see them no more, but we feel them as radiant heat; and when they attain lengths which are measured by yards and miles, they give the electrical phenomena.
A wide series of researches was evidently called into life by these researches,
of ether in a plane perpendicular to the
"molecular vortices," as he used to
Nature, vol. xxxix., p. 391, vol. xli., p. 295. + Ib. vol. xxxix., p. 548.
Prof. Lodge writes, in the Proceedings of the Royal Society (vol. l., No. 302, August 28, 1891): "This same discovery (Hertz's) would have been made by the audience at the Royal Institution on the evening of March 8, 1889, if it had not been made before; for, during a lecture on Leyden jars, every time one was discharged through a considerable length of wire, the heavily gilt wall paper sparkled brightly by reason of the incident radiation.
§ Comptes Rendus, 1891, t. 112, p, 1058; t. 113, p.
Sarasin et L. de la Rive in Comptes Rendus, 1891,
T See § 822 of Maxwell's Treatise on Electricity and
"Ueber die mechanischen Wirkungen electrischer
At the same time a further confirmation | mathematical and highly suggestive as of the light theory of electricity was given by Arons and Rubens, who proved that the relation which, according to Maxwell, ought to exist between the isolating power of various substances and their powers of refracting the rays of light, exists in reality. The resistance offered to the passage of light and that offered to the passage of electricity are connected by a simple relation. On the other side, Sir William Thomson read before the Royal Society a most interesting paper on the screens, and their efficiency against waves of different lengths. He demonstrated that if the electric sparks have a frequency of four or five per second, a clean white paper screen is sufficient to stop them; but when the frequency of the sparks is fifty, or more, the white paper screen makes no perceptible difference. If the paper is thoroughly blackened with ink on both sides, some moderate frequency of a few hundreds per second is, no doubt, sufficient to practically annul the effect of the interposition of the screen. For discharges following each other with frequencies up to one thousand millions in a second, a screen of blackened paper is perfectly transparent," but if we raise the frequency to five hundred million millions, the influence to be transmitted is light, and the blackened paper becomes an almost perfect screen." t As to the wonderful electrical effects produced by means of currents alternating with very high frequency, such as they are produced by the Montenegrin professor, Nikola Tesla, the readers of this review have already been familiarized with them in a preceding number (LIVING AGE, No. 2496, p. 309). Many more researches some of them
Drahtwellen," in Wiedemann's Annalen der Physik, 1891, vol. xlii., p. 405. Ritter and Rubens in same periodical, vol. xl. 1890. MM. Sarasin and De la Rive having come to the conclusion that the vibrators send out a great number of undulations of various periods, new researches were undertaken by Bjerkness (Archives des Sciences physiques et naturelles, 1891, t. 27, p. 229), and they brought to light the so-called "dampening "of electrical undulations-a question which also was discussed mathematically by Poincare (Archives, t. 25, p. 609), and Perot (Comptes Rendus.
January 25, 1892).
All the gases, many liquids, and many solids (glass,
gutta-percha, etc.) all named dielectrics - offer a
sage of electricity, and the relative amounts of this
regards the very structure of matter,* and some others opening new fields for experimental work, like J. J. Thomson's researches into the speed of propagation of the luminous discharge of electricity through a rarefied gas,† and Hertz's new experiments upon the transmission of the same discharges through various screens, transparent or not for light might be mentioned in connection with the above. But we must say, at least, a few words about the quite new lines of research indicated by Mr. Crookes's experiments on what he names "electrical evaporation." It was already known that an induction current, when passing through the platinum electrodes of a vacuum tube, tears off the molecules of platinum from the sphere of attraction of the wire, and transports them to a certain distance. Now, Mr. Crookes, comparing these phenomena with those of evaporation of liquids, made various experiments in order to determine the "evaporating" power of the electric stress under different circumstances and with different substances. He caused water to be transported in this way by the electric current; in order to increase the power of electricity upon metals, he diminished the cohesion of their molecules by heating the metals; and he studied also the relations between the transport of the molecules by electric stress, and the phenomena of phosphorescence.§ One feels, especially when remembering the speculations of the first half of this century (chiefly those of Séguin), that a new and most promising field is opened by these researches; they raise a host of questions relative to the most difficult parts of molecular mechanics.
The same must be said as regards mod. ern research in chemistry. The work now done is of two different kinds. While a numerous army of laboratory workers accumulate heaps and heaps of minute facts, and study the properties of separate chem ical compounds without being guided by any general idea, a few chemists devote themselves to the most intricate questions relative to the very substance of chemical reactions and molecular structure. They endeavor to bridge over the gulf between molecular physics and chemistry, and to
On some Test Cases for the Maxwell-Boltzmann Doctrine regarding Distribution of Energy, by Sir William Thomson, in Proceedings of the Royal Society, vol. 1., No. 302, p. 79.
+ Philosophical Magazine, 1890, vol. xxix.; Proceedings of the Royal Society, January 15, 1891. Annalen der Physik, 1892, Bd. 45, p. 28.
§ Proceedings of the Royal Society, vol. 1., p. 87.
conceive the latter as a separate branch of | of this work, and the recent researches of physics and mechanics. But we shall Strasburger, Flemming, Guignard, and postpone the analysis of these endeavors, Fol, while fully confirming the broad gen. hoping that some opportunity may soon eralizations laid at the foundation of modbe offered to come to some more definite ern biology, revealed a wide series of new ideas out of the conflicting theories of the facts having a direct bearing upon the present moment. question of heredity, which is so much debated now in connection with Weissmann's views.*
WHEN Schwann, closely following upon Robert Brown's and Schleiden's work, published in 1839 his famous "Microscopical Researches," and came to the conclusion that all possible tissues of both animals and plants consist of cells, or of materials derived from cells, it seemed that the primary units - the molecules, so to say-of which all living beings are built up, had finally been discovered. A small piece of structureless, granulated, jelly-like substance- the sarcode in animals and the protoplasm in plants-surrounded or not by a thin membrane, and containing a nucleus, this was the primary unit, giving origin to all the most complex and varied tissues.
It appeared, first, from the above-mentioned researches, that protoplasm itself consists of, at least, two different substances; one of them being a minute network of very delicate fibrils, while the other is an apparently homogeneous substance filling up the interstices between the network. Then it became evident that the nucleus which makes a necessary constituent part of cells, has a still more complicated structure, and that it plays a most prominent part in all the phenomena of subdivision of the cells and those of reproduction. It consists of a nuclear plasm, surrounded by a very thin membrane; it contains very often a still smaller nucleolus; and within the nuclear This conception evidently gave a for-plasm the microscope discovers extremely midable impulse to science and to scientific thin threads, or fibres, consisting in their philosophy altogether, the more so as it turn of extremely thin minute granules, or was soon followed by a most important spherules - the whole appearing as a ball discovery which established the close re- of thread coiled up somewhat roughly.t semblance existing between the subdivi. This being the usual aspect of the nucleus, sion of cells and the phenomena of sexual a series of modifications begin within it, reproduction in plants and animals. Twen- when the moment comes for a cell to sub ty-two years later, another still more divide. The nucleolus disappears; the important step was made in the same beaded threads, or fibres, shorten and bedirection, when Max Schultz published come thicker. They take the shape of his memoir, "Das Protoplasm," and minute hooks, and these hooks join toproved that the granular, jelly-like sub-gether (by the tops of the bendings) in one stance of the cells is identical in both the animal and vegetable kingdoms; that it is the very seat of all physiological activity, as it is capable of movement, of nutrition, of growth, of reproduction, and even of sensibility, or, at least, of irritability. Many must certainly remember the effect produced by the broad generalizations based upon Max Schultz's ideas by Haeckel in Germany and Mr. Huxley in this country, in his well-known lay sermon, "The Physical Basis of Life."
However, if protoplasm were the seat of physiological activity; if it could move, grow, reproduce itself, and display irritability, was it still to be considered as a "structureless, granulated jelly or slime"? It was a world in itself, and the microscope had to be directed towards the further study of this world. So it was, by Lionel Beale, Schultze himself, Strasburger, and most histologists of renown. Discovery upon discovery was the reward
point, the pole. By the same time the membrane of the nucleus is reabsorbed, and the surrounding protoplasm of the cell penetrates within the nucleus, thus mixing up together with the nuclear plasm. Thereupon a most important change fol
Strasburger, Ueber Kern und Zell Theilung im botanique de France, 1890, t. 36, and Comptes Rendus, Pflanzenreiche, Jena, 1888; Guignard, in Bull. Soc. 1891, t. 112, pp. 539, 1074, and 1320; t. 113. p. 917; 1891, Bd. 37, P. 249, and Anatomischer Anzeiger, W. Flemming in Archiv für mikrosk. Anatomie, 1891, p. 78. An immense literature has suddenly grown up upon this subject. Excellent résumés of the whole question have been given in English, up to 1888, by Prof. McKendrick in Proceed. Glasgow Philos. Soc., vol. xix. ; and to the end of 1890 by Sir William Turner, in an address, "The Cell Theory, Past and Present,' delivered in October, 1890, before the Scottish Micro
scopical Society (Nature, vol. xliii., p. 11 and sq.)
†The albuminous matter of which these threads con
sist received the name of "nuclein," and the threads themselves were named "chromatin fibres," owing to their affinity to coloring matter. The transformations in the nucleus which have just been described received the general name of "karyokinesis," or "nuclear movement." The names, as seen, are simply descrip tive.
lows. Each of the thickened nuclein | is now formed by both coalesced nuclei, fibres, or threads, splits in its length, and surrounded by a radiation of the fibrils of the number of the threads being thus protoplasm. Then begins what Fol names doubled, one-half of them is attracted" the quadrille of the centres." Each of towards a radiated spindle-figure in one part of the cell, while the other half arranges in the same way in its opposite part. The two radiated figures thus separate, and only then (if the nucleus subdivides in giving origin to two new cells) a membrane, or parts of a membrane, grow between the two. After the separation, the fibres either coalesce with their ends, or return in the shape of a ball of thread.
It is a whole world undergoing a whole cycle of modifications. And yet this is not all. It appears from Strasburger's work that all the cells are not quite similar, but that the number of nuclein fibres varies from eight to twelve and to sixteen in various families of plants, the individuality of the types thus seemingly depending upon their number; while Guignard found that with several plants the cells which will be destined, after the division of the mother cell, to become the reproductive organs will always have but one-half of the normal number of fibres (say twelve), while those which are destined to become the vegetative organs will have the full number say, twenty-four. The former will acquire the full number of fibres only after fecundation. Are, then, the cells differentiated from the first moment of their bi-partition? And what part does the number of chromatin fibres play in that differentiation?
Further complications are discovered through the study of the protoplasm itself. It was known some time ago that there are, in the animal cells, two peculiar spots, surrounded by rays of sarcode, which were named spheres of attraction, or directing spheres, or centrosomata, or simply "centres."
The same minute centres have now been found by Strasburger and Guignard in vegetable cells also, and it appears that these bodies, essentially belonging to the protoplasm - not to the nucleus -take a leading part in the phenomena of reproduction. Professor Fol, who carried on his researches with eggs of sea-urchins, saw that when the elements of the male cell have entered the female cell, the centre of the former separates from the top of its nucleus and joins the centre of the latter. Both lie close to one another; then they become elongated and take positions on the opposite sides of the nucleus, which
Report upon which the Prix Bordin was awarded to Guignard, in Comptes Rendus, December 21, 1891,
them divides into two half-centres, and all four move, so that each half-centre of the male cell meets and coalesces with one half-centre of the female cell, and the two newly formed centres become the poles of attraction for the spindles of the nucleus. The act of fecundation is thus not a simple coalescence of two nuclei, originated from two separate individuals, as was supposed before; it also consists of the union of each two of the four half-centres originated in the protoplasm.
The interest attached to these minute changes is great, on account of their consequences as regards the theory of heredity. The observations of Fol, and the quite analogous observations of Guignard as regards plants, would only confirm the doubts expressed by Sir William Turner in his address before the Microscopical Society, as to the germ plasm being "so isolated from the cells of the body generally as to be uninfluenced by them, and to be unaffected by its surroundings;" and they would give further weight to its restrictions as regards Weissmann's theory of heredity. However, the questions at issue are so complicated and so delicate, that further research is wanted, and eagerly expected by specialists.
But what is protoplasm itself? What is this jelly-like matter which exhibits all phenomena of life? Science has not yet given a positive answer to this great question. On the one side, we have the germs of an opinion, shared by some biologists who are inclined to see in protoplasm an aggregation of lower organisms. Thus R. Altmann † and I. Straus ‡ consider that the granulations of protoplasm are the essential and fundamental elements of the organic being. As to the cell, it is not, in Altmann's view, an elementary organism, but a colony of elementary organisms which group together according to certain rules of colonization. They constitute the protoplasm as well as the nuclear plasm, and they are the morphological units of all living matter. These granules, he maintains, are identical with microbes; their shape, their chemical reactions, their movements, and their secretory functions are similar; but the granules of the pro
toplasm differ from bacteria in not being capable of a separate existence. They can only live in cells. It is absolutely impossible to say, at the present time, how far this view may find support in ulterior research, though it must be mentioned that it is derived from elaborate investigations into the cells of various glands and their secretions, and that it finds support in facts accumulated by many well-known anatomists. It must also be added that some biologists namely, J. C. Vogt-go a step further and maintain that all micro-organisms, and all cells of more complicated organisms, are structures of a fourth or higher order; they are colonies of "polyplasts," which themselves consist of "monoplasts," or those granules which are distinguished in the protoplasm and the nuclear plasm. But, on the other side, we also have the other extreme view, supported by the authority of Professor O. Bütschli, who sees in protoplasm nothing but a foam, quite similar to the foams which may be artificially produced, and who maintains that all phenomena observed in living protoplasm are simply physical and chemical processes.
The great question as to what protoplasm is, evidently will not be solved soon. But the above-mentioned researches will give an idea of the problems which at this moment absorb the attention of biologists. One important step has certainly been made: the complicated structure of protoplasm has been recognized, and the exploration of the vital processes in "living matter" now stands on a firm footing.‡
IT is known that Darwin, when he be gan thinking about the possible origin of the eye, used to feel a kind of shudder in consequence of the difficulties standing in the way. An important step towards smoothing these difficulties has now been made by Professor S. Exner, who has brought out an elaborate and richly illustrated work on the eyes of crustaceans and insects, and by Mr. Watase, who has studied the question as to their possible
The author names Gianuzzi, Ranvier, Renaut, and partly Henri Martin.
Das Empfindungsprinzip und das Protoplasma, auf Grund eines einheitlichen Substanzbegriffes, Leipzig, 1891; Journal of the Microscopical Society, February, 1892.
Prof. R. Greef's exploration of the motor-fibrils of the Amaba terricola (Biologisches Centralblatt, November, 1891, pp. 599 and 633) may be mentioned as an illustration of such researches.
Die Physiologie der facetiten Augen von Krebsen und Insecten, Leipzig, 1891.
origin. The compound eye coasists, as known, of hundreds and thousands of separate conical, almost cylindrical, parts, each of which corresponds to a separate eye; however, their structure widely dif fers from that of the mammalian eye. Each of the component eyes has, like ours, a cornua, but it is flat, and the crystalline part of the eye has not the shape of a lens, but of a "lens cylinder," that is, of a cylinder which is composed of sheets of transparent tissue, the refracting powers of which decrease towards the periphery of the cylinder. If an eye of this kind is removed and freed of the pigment which surrounds it, objects may be looked at through it from behind; but its field of vision is very small, and the direct images received from each separate eye are either produced close to one another on the retina (or rather the retinulæ of all the eyes) or superposed. In this last case no less than thirty separate images may be superposed, which is evidently a great advantage for nocturnal insects. Many other advantages are derived from the compound structure of the insect eye. Thus the mobile pigment which corresponds to our iris cau take different positions, either between the separate eyes or behind the lens cylinders, in which case it acts as so many screens to intercept the over-abundance of light. Moreover, it has been ascertained by Exner that with its compound eye the common glow-worm (Lampyris) is capable of distinguishing large sign-board letters at a distance of ten or more feet, as also extremely fine lines engraved or of an inch apart, if they are at a distance of less than half an inch from the eye. As a rule, the compound eye is inferior to the mammalian eye for making out the forms of objects, but is superior to it for distinguishing the smallest movements of objects in the total field of vision.
All stages of evolution of the eye may be studied among the insects and the Arachnides. Thus, beginning with the eye of the Limulus, Mr. Watase shows how it may have originated from a simple minute cavity in the epithelium. The sensitive cells lie in direct continuity with those of the epithelium, or hypodermis; and a cavity, with a pigment cell therein, and covered by epithelium, may represent the first rudiment of the eye. Later on the cavity deepens, and the roughly con
"On the Morphology of the Compound Eye of the Anthropodes," in "Studies from the Biological Laboratory, Johns Hopkins University," vol. iv. (Baltimore).