of cells, was no longer a matter of doubt to me, and further observation has entirely confirmed this view. The microscope has shown me that all the varied forms in the animal tissues are nothing but transformed cells, that uniformity of texture is found throughout the animal kingdom, and that in consequence a cellular origin is common to all living things. All my work has authorised me to apply to animals as to plants the doctrine of the individuality of cells."' The first matter in connection with cells that we shall take up is one which is not strictly a chemical one, but one which can nevertheless not be omitted in a consideration of the physiology of cells; this is the physiology of protoplasmic movement. PROTOPLASMIC MOVEMENT This section is very largely an abstract of Engelmann's article on this subject in Hermann's Handwörterbuch der Physiologie.' The movement of living protoplasm must be classed with muscular and ciliary movement, with which it is closely connected by numerous transitional forms, as phenomena of contractility. The special character of protoplasmic movement lies in this, that the particles of the contractile mass move, not in relation to any fixed position of equilibrium, but as do the moving particles of a fluid. Transitional forms of movement between this and the highly ordered and limited contraction of a muscle occur, and of these the following are instances: the movements of the tentacles of acinetæ,2 the superficial sarcode of sponges,3 the endothelial cells of young blood capillaries, the pigment cells of amphibians and reptiles, and many others. The oldest description of a protoplasmic movement is that by von Rosenhof (Monatlich herausg. Insectenbelustigung, 3ter Th. p. 621. Nürnberg, 1755) of a fresh-water Amœba. Twenty years later came Corti's (Lucca, 1774) description of the rotation of the cell sap in Chara. In the early part of the present century the wide distribution of this phenomenon in vegetables was demonstrated by Meyer, R. Brown,7 Amici and others. Then came Dujardin's* description of the movements of the body substance of certain rhizopod 1 Translated by A. G. Bourne, D. Sc.: Quart. Journal Micr. Sci. xxiv. 369. * Lieberkühn, Bewegungerschein. d. Zellen, p. 346. Marburg, 1870. 3 Stricker, Wiener Sitzungsb. d. Math. naturw. Cl. lxxiv. p. 313, 1877, and others. 4 G. Seidlitz, Beiträge zur Descendenztheorie, p. 31–36, Leipzig, 1876, 5 Hering, Cent. f. med. Wissens. 1869, No. 4, p. 49. 6 In Vallisneria, 1827. 7 In Tradescantia, 1830. 8 Bull. de la soc. des sci. nat. de France, 1835, No. 3. Ann. sci. nat. iii. 2nd sér. p. 312, 1835. iv. p. 343, 1835. The movement of white animals. This substance he termed sarcode. blood corpuscles was first observed by Wharton Jones in 1846. V. Mohl2 gave the name protoplasm to the motile substance in plant cells, and Cohn3 first advanced the suggestion that this and sarcode were identical. The actual identity of animal and vegetable protoplasm was more clearly proved by Max Schultze, de Bary," Haeckel, Kühne and others; and a more complete knowledge concerning its movement has been afforded by Nägeli, Brücke, and Heidenhain. The wandering of amoeboid cells in animal tissues was brought into general notice by v. Recklinghausen, and the importance of this in physiological and pathological process was shown by Stricker and Cohnheim. The movements of naked protoplasm may be distinguished into three types-amoeboid, streaming, and gliding. Amoeboid movement shows itself in the protrusion and retraction of conical and at first generally hyaline processes, into which the granules from the interior stream in and cut. The processes may ramify and even form networks. If the processes fasten themselves to fixed bodies, they can by shortening draw the rest of the protoplasm after them, and so produce a movement of translation. These movements may be readily seen in white blood corpuscles, in many unicellular animals, in numerous ova (hydra, sponges, &c.), in connective tissue cells, and in the plasmodium of myxomycetes, where the movements are visible to the naked eye. Streaming movement occurs in many protozoa (Heliozoa, Radiolaria, &c.). Out of the protoplasmic body long thin threads of protoplasm spring, and upon their surface a great number of fine granules in active streaming movement are seen, the main substance of the threads themselves often showing no movement, or only slow changes of form. Gliding movement : in this case, extremely thin layers of protoplasm devoid of granules move along outside a firm cell wall, and by means of this movement the whole body progresses over a firm substance in a gliding or creeping manner. The rapidity of the movement seldom exceeds 0:04 mm. in a second. This form of movement is well seen in the diatoms. The movements of cells bounded by firm integuments. This case is chiefly realised in vegetable cells, and botanists distinguish two varieties (1) Circulation, in which contractile protoplasmic threads 1 Proc. Roy. Soc. 1846. 5 Nova Acta Leop. Caes. xxii. 2. p. 605, 1850. 2 Bot. Zeitung, p. 73, 1846. 4 Arch. f. Anat. u. Physiol. 1858, p. 330; 1861, p. 1. 5 Zeit. f. wiss. Zool. x. p. 88. 6 Die Radiolarien, Berlin, 1862. Zeit. wiss. Zool. xv. p. 342, &c. 7 Unters. ü. das Protoplasma, Leipzig, 1864. Arch. f. Anat. u. Physiol. 1859, p. 564. Arch. f. path. Anat. xxviii. p. 157, 1863. stretch inwards from the cell wall, traversing the cell space, which is filled with fluid; these threads divide, fuse, form sheets and generally exhibit streaming granules. These movements are well seen in the staminal hairs from Tradescantia; and in the animal kingdoms in Noctiluca, tentacles of medusæ, gill fibres of Branchiomma, &c. (2) Rotation: here the protoplasm lining the cell walls rotates as a connected mass round the interior of the cell, generally following constant tracks and with an even velocity; chlorophyll grains, crystals, nuclei, &c., are carried with it. This is well seen in many vegetable cells like Vallisneria, and here also must be classed the rotation of the endoplasm of Paramecium and Vorticella. General conditions of protoplasmic movement. (a) Temperature. Speaking generally, the movement ceases below 0°C. and above 40°C. Within these limits the velocity of the movement increases with the temperature. The optimum temperature is generally a few degrees below the maximum temperature compatible with movement. When warmed to the maximum, naked cells become spherical. When subsequently cooled the protoplasm does not resume movement, as the contained proteids have been coagulated by the heat, and the protoplasm is dead. When protoplasm enters suddenly into heat-rigor, as by a jet of steam playing upon it, it has no time to change its form, but remains in the position it had the moment before death. A low temperature on the other hand, though it stops movement, does not kill the protoplasm; even after actual freezing, protoplasm will when thawed resume movement. Kühne lowered Tradescantia hairs to -14°C. for five minutes, and after careful thawing the threads were again found in active streaming movement. Animal life in its simplest form seems to withstand great cold without apparent injury; thus McKendrick and Coleman' exposed bacterial spores to a temperature of -83° for 100 hours, without succeeding in killing them. (b) Imbibition water acts like a degree of temperature. There is a maximum (over 90 per cent.) and a minimum (below 60 per cent.) for the amount of contained imbibition water at which movements stop. When the maximum is gradually approached, the protoplasmic mass becomes spherical; removal of the excess of water with indifferent substances like saline solutions often cause the movements to be reinduced after even some minutes of water-rigor. The withdrawal of water produces a temporary or permanent dry-rigor. Lower organisms like spores, encysted amabæ, &c., may be dried and kept for years in this condition; after that time on the application of moisture they resume activity. 1 Proc. Royal Instit. of Great Britain, May 29, 1885. (e) Oxygen.-Withdrawal of oxygen ultimately produces death, but in media free from oxygen, protoplasmic movement will continue for some hours, the cells giving off carbonic anhydride. The oxygen previously taken into the cell is in a state of loose combination; when however this storage oxygen is exhausted the cell dies. (d) Poisons.-A slight excess of acid, and a rather larger quantity of alkali, causes a cessation of protoplasmic movement, which can be counteracted for a time by neutralisation. A very weak alkali stimulates the movement. Carbonic acid gas, ether, and chloroform vapour stop it. Veratrine (Kühne) and quinine (Binz) 1 act similarly. (e) Artificial stimulation. The following may be used as stimuli to movement: weak electrical currents, or sudden alterations of temperature, within the temperature range of contractility; in the case of most cells, light does not act as a stimulus; in other cases it does; for instance the Pelomyxa moves actively in the dark, and becomes spherical when exposed to light; plant cells containing chlorophyll are most susceptible to the influence of light. Mechanical stimuli like pressing, bruising, tearing, &c., and chemical stimuli like ammonia vapour, various strengths of saline solutions, &c., may also be employed; as a rule, however, in chemical stimulation, accessory phenomena like shrinking,. swelling, or coagulation interrupt and mask the effect of the excitation. Theoretical conclusions. Protoplasm must be regarded as an aggregate of exceedingly minute, contractile, excitable form-elements, and the movement as a whole is the result of the changes in form of these very small elements. The nature and cause of the changes in form of the latter remains provisionally undetermined. With regard to their form we may take it for granted that when in a condition of maximal excitation they are almost spherical, and when not excited are generally elongated or thread-like. The mechanical behaviour of naked protoplasm teaches us that the changes in form must take place with a force which exceeds, as a rule, the force which the elements, if they were fluid, would put forth, in order to assume a spherical form. These contractile elements may be called 'Inotagmata.' Probably they are positive uniaxial doubly refracting.2 The active as well as the passive phenomena of protoplasmic movement compel us further to make the assumption that the inotagmata of protoplasm are not like those of muscles and cilia arranged in a relatively firm manner with their axes in one definite direction, but are fastened together loosely and are capable of moving one against. 1 Arch. mikr. Anat. iii. p. 383, 1867. 2 Contractilität und Doppelbrechung, Pflüger's Arch. xi. 1875. the other in all directions; still the possibility of a temporary or permanent grouping of a greater or less number of inotagmata into definitely shaped larger masses (fibres, networks, membranes, &c.) is not excluded. As a reason for the possibility of alteration of arrangement of the protoplasmic particles, and in connection with the prevailing views concerning the molecular structure of organised masses, we must assume the existence of a capability for the imbibition of important quantities of water between the inotagmata, and the larger masses or inotagma groups. The motility, as already shown, increases or diminishes with the quantity of this water. PHYSICAL AND CHEMICAL PROPERTIES OF PROTOPLASM Engelmann describes contractile protoplasm as a homogeneous, transparent, almost always colourless mass, with a higher refractive index than water, but lower than oil. In some cases where it has the form of fibres or thin layers with a prevailing movement in one direction, it is doubly refracting, and as in muscles and cilia with a single positive axis, the optical axis coincides with the direction of the movement. Different portions of the same protoplasmic mass may have different refractive powers, and during movements the refractive power of the same portion changes to a considerable extent. Protoplasm is semifluid, does not mix, but swells up with water; it is cohesive and extensible. Though the superficial layers of many cells are firmer than the interior, a distinct membrane is absent as a rule in animal cells. Protoplasm, almost without exception, contains granules which play a passive rôle in movement. The granules are albuminous, fatty, and in some cases inorganic (e.g. calcium carbonate in certain Myxoplasmodia) in nature. Often the exterior portions of the cell (exoplasm) are free from granules, while they are present in large quantities in the internal regions (endoplasm). The irregular shaking, dancing motion of these particles, called the 'Brownian movement,' must not be mistaken for vital movements. In addition to granules, protoplasm in vegetable cells always, in animal cells often, exhibits vacuoles or spaces filled with a watery liquid. These are globular in resting protoplasm, but may become drawn out during movement. The same holds good for gas bubbles, which occur occasionally in protoplasm. 1 Quart. J. Mic. Science, xxiv. 373. 2 |