Quain's Elements of anatomy ... Vol.2. Part 1 : Microscopic anatomy / by E.A. Schafer.

Date:
1912
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Licence: In copyright

Credit: Quain's Elements of anatomy ... Vol.2. Part 1 : Microscopic anatomy / by E.A. Schafer. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    and nucleus is composed of an aggregate of microscopic particles, each of which is capable of multiplying and functioning independently. This independence has been ascribed to particles or granules which are often seen in protoplasm (‘ microsonies ’ of Hanstein), and to accentuate this view they were termed by Altmann' ‘bioplasts’ or ‘elementary organisms.’ Altmann attempted to establish the identity of his elementary organisms with the obvious granules which have long been recognised in cells, and which have frequently been regarded as merely adventitious in character or as products of cell-activity ; not, as Altmann regards them, as the actual living material and the cause of activity. Altmann’s view has not hitherto met with general acceptance by biologists, although it cannot be doubted that it is a very common character of the protoplasm of many cells to exhibit, even in the living condition, granules of protein substance, which may be so closely packed as to occupy the greater part of the cell (see pp. 22 to 24). Apart from visible ‘ granules,’ there are strong grounds for believing that living substance is composed of ultramicroscopic particles,^ each of which is probably constituted of a central more solid and a peripheral fluid portion. Such theoretical particles, which are themselves not molecules but groups of molecules, have been variously named micellae (Nageli), inotagmata (Engelmann), biophores(Weismann), biogens (Verworn) and they are assumed to fulfil all the functions of protoplasm (or rather of bioplasm), having specific characters in different cells, and being subject to metabolic processes, to growth and multiplication, and to rearrangement within the cell, so as to produce changes of form and structure of nucleus and protoplasm, and eventually cell-division. Those biophores, or groups of biophores, which constitute the nuclear chromatin of the germ- cells are assumed by Weismann to include representatives of all the specific biophores of the somatic cells, and they are regarded by him as being the transmitters of hereditary qualities ; subject to variation and to increase or decrease in relation to one another according to the varying conditions to which they are exposed. The term germinal selection is used by Weismann to denote the result of such influences upon the biophore groups.'* THE PROTOPLASM OF THE CELL. The living substance of cells, both plant and animal, is termed bioplasm. That part which constitutes the nucleus is known as haryoplasm; that which is present in the cell outside the nucleus is protoplasm; while a specialised portion, which is connected with the centrosome, is termed archoplasrn. The whole sub- stance of the cell apart from the nucleus is often alluded to as cytoplasm. Under this name other materials than those which constitute the living substance are in- cluded. The presence of such materials occurs, indeed, in certain cells to so great an extent that the protoplasm itself, of which the whole cell-substance in the embryonic cell was originally constituted, has become reduced to a relatively small proportion ; indeed, even in cells of the same kind in different species of animals and plants, the size of the cell varies directly with the amount of non-protoplasmic material which has become accumulated within the cell. A notable example of this is met with in the ovum, which in some animals, including man, is minute and even microscopic; 'Whereas in others, such as the bird, it attains a larger size than any other cell in the body. There may doubtless be an absolutely larger amount of protoplasm in the larger cell, but relatively to the non-protoplasmic material the actual protoplasm occurs in very much smaller amount (see vol. i. p. 9). Various names [paraplasm, deuteroplasm) have been proposed for the non-protoplasmic contents of cells, which may consist merely of watery fluid, as in the cell-sap of plants—or of any con- ceivable organic material, such as granules of starch, globules of oil, or crystals of protein matter or of haemoglobin; but it is to be doubted whether anything is gained by including materials so diverse under a single designation. Examined chemically, protoplasm can be resolved into (1) water, which constitutes from two-thirds to three-fourths of its weight ; (2) organic material which exhibits the properties of proteins or protamines, combined usually, perhaps invariably, with a certain proportion of a phosphorus and iron containing substance known as nuclein, forming nncleo- • Ludwig Festschrift, 1887 ; Die Elementarorgauismen, Leipzig, 1890 ; 2nd edition, 1894. ^ Not necessarily the particles which are rendered visible by the ultramicroscope. For an account of these, see W. Biedermann, Ergebn. d. Physiol, viii. 1909. 2 Die Biogenhypothese, 190M. See also his Allgemeine Anatomie, 1908. • Weismann, The Evolution Theory, transl. by A. and M. B. Thomson, 1904. See also T. H. Bryee, Embryology (vol. i. of this work), p. 20.