444 



NA TURE 



[September 6, 1900 



"tissues. Subsequently Heidenhain and other histologists have 

 recorded similar observations. It would seem, therefore, as if 

 there were reason to regard the centrosome, like the nucleus, as 

 a permanent constituent of a cell. This view, however, is not 

 universally entertained. If not always capible of demonstration 

 in the resting stage of a cell, it is doubtless to be regarded as 

 potentially present, and ready to assume, along with the 

 radiations, a characteristic appearance when the process of 

 nuclear division is about to begin. 



One can scarcely regard the presence of so remarkable an ap- 

 pearance as the achromatic figure without associating with it an 

 ■important function in the economy of the cell. As from the 

 •centrosome at the pole of the spindle both sets of radiations 

 diverge, it is not unliuely that it acts as a centre or sphere of 

 ■energy and attraction. By some observers the radiations are 

 regarded as substantive fibrillar structures, elastic -or even con- 

 tractile in their properties. Others, again, look upon them as 

 morphological expressions of chemical and dynamical energy in 

 the protoplasm of the cell body. On either theory we may* 

 assume that they indicate an influence, emanating, it may be, 

 from the centrosome, and capable of being exercised both on the 

 cell plasm and on the nucleus contained in it. On the contrac- 

 tile theory, the radiations which form the body of the spindle, 

 either by actual traction of the supposed fibrillteor by their pres- 

 sure on the nucleus which they surround, might impel during 

 karyokinesis the dividing chromosome elements towards the 

 poles of the spindle, to form there the daughter nuclei. On the 

 <lynamical theory, the chemical and physical energy in the 

 centrosome might influence the cell plasm and the nucleus, and 

 attract the chromosome elements of the nucleus to the poles of 

 the spindle. The radiated appearance would therefore be con- 

 sequent and attendant on the physico-chemical activity of the 

 centrosome. One or other of these theories may also be applied 

 to the interpretation of the significance of the polar radiations. 



t 

 Cell Plasm. 



In the cells of plants, in addition to the cell wall, the cell body 

 and the cell juice require to be examined. The material of the 

 cell body, or the cell contents, was named by von Mohl (1846) 

 .protoplasm, and consisted of a colourless tenacious substance 

 which partly lined the cell wall (primordial utricle), and partly 

 traversed the interior of the cell as delicate threads enclosing 

 spaces (vacuoles) in which the cell juice was contained. In the 

 protoplasm the nucleus was embedded, Nageli, about the same 

 time, had also recognised the difference between the protoplasm 

 and the other contents of vegetable cells, and had noticed its 

 nitrogenous composition. 



Though the analogy with a closed bladder or vesicle could i)o 

 longer be sustained in the animal tissues, the name " cell " con- 

 tinued to be retained for descriptive purposes, and the body of 

 the cell was spoken of as a more or less soft substance enclosing 

 a nucleus (Leydig). In 1861 Max Schultze adopted for the 

 substance forming the body of the animal cell the term " pro- 

 toplasm." He defined a cell to be a particle of protoplasm 

 in the substance of which a nucleus was situated. He re- 

 garded the protoplasm, as indeed had previously been 

 pointed out by the botanist Unger, as essentially the same as the 

 contractile sarcode which constitutes the body and pseudopodia 

 of the Amoeba and, other Rhizopoda. As the term " proto- 

 plasm," as well as that of "bioplasm" employed by Lionel 

 Beale in a somewhat similar though not precisely identical sense, 

 ■involves certain theoretical views of the origin and function of 

 the body of the cell, it would be better to apply to it the more | 

 purely descriptive term " cytoplasm " or "cell plasm." i 



Schultze defined protoplasm as a homogeneous, glassy, tena- 

 cious material, of a jelly-like or somewhat firmer consistency, in | 

 ■which numerous minute granules were embedded. He regarded 

 it as the part of the cell especially endowed with vital energy, 

 whilst the exact function of the nucleus could not be defined. 

 Based upon this conception of the jelly-like character of pro- 

 toplasm, the idea for a time prevailed that a structureless, dimly 

 granular, jelly or slime destitute of organisation, possessed great 

 physiological activity, and was the medium through which the 

 phenomena of life were displayed. 



More accurate conceptions of the nature of the cell plasm soon 

 began to be entertained. Briicke recognised that the body of 

 •the cell was not simple, but had a complex organisation. Flem- 

 ming observed that the cell plasm contained extremely delicate 

 'threads, which frequently formed a network, the interspaces of 

 which were occupied by a more homogeneous substance. Where 



the threads crossed each other, granular particles (mikrosomenj 

 were situated. Butschli considered that he could recognise in 

 the cell plasm a honeycomb-like appearance, as if it consisted 

 of excessively minute chambers in which a homogeneous, more 

 or less fluid, material was contained. The polar and spindle- 

 like radiations visible during the process of karyokinesis, which 

 have already been referred to, and the presence of the centro- 

 some, possibly even during the resting stage of the cell, furnished 

 additional illustrations of differentiation within the cell plasm. 

 In many cells there appears also to be a difference in the 

 character of the cell plasm which immediately surrounds the 

 nucleus and that which lies at and near the periphery of the cell. 

 The peripheral part (ektoplasma) is more compact and gives a 

 definite outline to the cell, although not necessarily differentiating 

 into a cell membrane. The inner part (endoplasma) is softer, 

 and is distinguished by a more distinct granular appearance, 

 and by containing the products specially formed in each par- 

 ticular kind of cell during the nutritive process. 



By the researches of numerous investigators on the internal 

 organisation of cells in plants and animals, a large body of 

 evidence has now been accumulated, which shows that both 

 the nucleus and the cell plasm consist of something more,than a 

 homogeneous, more or less viscid, slimy material. Recognisable 

 objects in the form of granules, threads or fibres can be distin- 

 guished in each. The cell plasm and the nucleus respectively 

 are therefore not of the same constitution throughout, but possess 

 polymorphic characters, the study of which in health and the 

 changes produced by disease will for many years to come form 

 important matters for investigation. 



Function of Cells. 



It has already been stated that, when new cells arise within 

 pre-existing cells, division of the nucleus is associated with 

 cleavage of the cell plasm, so that it participates in the process 

 of new cell-formation. Undoubtedly, however, its rdle is not 

 limited to this function. It also plays an important part in 

 secretion, nutrition, and the special functions discharged by 

 the cells in the tissues and organs of which they form 

 morphological elements. 



Between 1838 and 1842 observations were made which showed 

 that cells were constituent parts of secreting glands and mucous 

 membranes (Schwann, Henle). In 1842 John Goodsir com- 

 municated to the Royal Society of Edinburgh a memoir on 

 secreting structures, in which he established the principle that 

 cells are the ultimate secreting agents ; he recognised in the cells 

 of the liver, kidney, and other organs the characteristic secre- 

 tion of each gland. The secretion was, he said, situated between 

 the nucleus and the cell wall. At first he thought that, as the 

 nucleus was the reproductive organ of the cell, the secretion was 

 formed in the interior of the cell by the agency of the cell wall ; 

 but three years later he regarded it as a product of the nucleus. 

 The study of the process of spermatogenesis by his brother, 

 Harry Goodsir, in which the head of the spermatozoon was 

 found to correspond with the nucleus of the cell in which the 

 spermatozoon arose, gave support to the view that the nucleus 

 played an important part in the genesis of the characteristic 

 product of the gland cell. 



The physiological activity of the cell plasm and its complex 

 chemical constitution soon after began to be recognised. Some 

 years before Max Schultze had published his memoirs on the 

 characters of protoplasm, Briicke had shown that the well- 

 known changes in tint in the skin of the Chamseleon were due 

 to pigment granules situated in the cells in the skin which were 

 sometimes diffused throughout the cells, at others concentrated 

 in the centre. Similar observations on the skin of the frog 

 were made in 1854 by von VVittich and Harless. The move- 

 ments were regarded as due to contraction of the cell wall on 

 its contents. In a most interesting paper on the pigmentary 

 system in the frog, published in 1858, Lord Lister demonstrated 

 that the pigment granules moved in the cell plasma, by forces 

 resident within the cell itself, acting under the influence of an 

 external stimulant, and not by contractility of the wall. Under 

 some conditions the pigment was attracted to the centre of the 

 cell, when the skin became pale ; under other conditions the 

 pigment was diffused throughout the body and the branches of 

 the cell, and gave to the skin a dark colour. It was also 

 experimentally shown that a potent influence over these move- 

 ments was exercised by the nervous system. • 



The study of the cells of glands engaged in secretion, even when 

 the secretion is colourless, and the comp.irison of their appear- 



NO. 1610, VOL. 62] 



