Images de page
[blocks in formation]
[ocr errors][ocr errors]
[ocr errors]
[ocr errors]
[merged small][ocr errors]

the bishop is told he must be the husband of children, and provided for them out of the property
one wife, and rule his household and his children of the church. Avaricious princes and prelates
well; and 'forbidding to marry' is reckoned made traffic of the concubinage of the lower clergy
among the doctrines of devils. But a remote by levying a species of blackmail, under the name
sanction for the later discipline has been sought of fines, on the tacit understanding that the focaria,
for in the regulations of the Jewish priest or occupant of the priest's hearth, should not be
hood. The Mosaic law forbade priests to marry disturbed. At the time of the Council of Trent,
divorced women or harlots, and enjoined continence the Emperor Charles, in the expectation that some
upon all when preparing to offer sacrifice. Jerome relaxation would be made in the laws on the sub-
argues that the Christian priest should offer sacrifice ject, permitted in 1548, by the arrangement known
daily, and should therefore be perpetually con as the Interim, married priests to retain their wives
tinent; and Pope Siricius (385 A.D.) insists that until the council should come to a decision. The
marriage was permitted to the priest of the old law Emperor Ferdinand a little later (1562) urged upon
only because the sacerdotal order was then limited the same council the abrogation of celibacy. But
to the tribe of Levi, but now that the tribal restric the Catholic reaction was too strong, and the
tion is removed, the license is abrogated also. council in November 1563 pronounced, " If any one

The ecclesiastical legislation on celibacy was de- shall say that clerks constituted in holy orders, or
veloped gradually and unequally in the several regulars who have solemnly professed chastity, are
parts of the church. In the 2d century it became a able to contract matrimony, or that, being con-
pious custom to make vows of chastity, and it was tracted, such matrimony is valid . . . let him be
thought becoming in the higher clergy to renounce anathema.'
matrimony; and although there are examples of It should be observed, however, that in the United
bishops and priests in the first three centuries living Greek Church Rome tolerates a married clergy-
with their wives and begetting children, it has been i.e. a man already married may be ordained priest,
confidently asserted that no instance can be quoted and continue to live with his wife, though con-
of a marriage contracted at this period after ordina tinence is imposed upon him at certain times. It is
tion. The obligations of the marriage contract the custom for the young candidate for orders to
were, however, considered sacred ; and the Apostolic leave the seminary for a while to get a wife, and
Canons impose the penalty of deposition on bishop, then return for ordination. If he should become
priest, or deacon, who should separate from his wife a widower, he cannot of course marry again, and

under the pretence of piety.' At the end of the no married priest can be made a bishop.' The
3d and beginning of the 4th century, marriage after bishops are therefore, as a rule, taken from the
ordination was prohibited by formal legislation. A monasteries,
further and important step was taken in the year Since the Council of Trent, the observance of
305 by the Spanish council of Elvira, which decreed celibacy has been comparatively well maintained.
that sacred ministers who were already married, This is especially true of those countries where the
should live in continence. At the Council of Nicæa | Catholic community is mixed with or surrounded
an attempt was made to impose this new rule upon by Protestant neighbours, and watched by a vigi-
the whole church, but it was frustrated by the lant press. Away from the high-roads of civilisa-
opposition of a venerable monk, Paphnutius, him tion, in Mexico, Brazil, and other parts, concubinage
self a celibate; and the law to this day has never has again become the rule, less openly perhaps, but
been accepted in the Eastern Church. In the West, quite as obstinately as in the middle ages.
however, a series of synodal enactments and papal The moral loss or gain to the church from her dis-
decrees established or renewed the more rigorous cipline in this matter is a question of controversy
rule. But in no matter of ecclesiastical discipline which from time to time has been raised within her
must the distinction between theory and practice own communion. But the attention paid by biolo-
be more carefully observed. The clergy everywhere gists to the hereditary transmission of human
resisted the law, and resisted with considerable faculties and dispositions has recently exhibited
success. St Patrick, who tells us that his father the effects of celibacy in a new light. Mr Galton
and grandfather were in holy orders, when laying has remarked that the Roman Church has acted
down rules in one of his Irish synods for the con as if she 'aimed at selecting the rudest por-
duct of his clergy, directs that their wives should tion of the community to be alone the parent of
keep their heads covered. In the province of future generations. The policy which attracts men
Milan, indeed, the marriage of priests continued to and women of gentle natures fitted for deeds of
be perfectly legal. Discipline and usage varied in charity, meditation, or study to the unfruitful life
different countries, but it may be safely said that of the cloister and the priesthood, appears from
for many centuries the celibacy of the uncloistered this point of view to be singularly unwise and
clergy was little more than å pious fiction, until suicidal,' tending, as it must, though by impercep-
Hildebrand, afterwards Gregory VII., by his great tible degrees, to the deterioration of the race. To
influence and vigorous measures, secured a more the enforcing of this discipline in Spain, for ex-
strict observance of the rule.

ample (coupled with the cutting off of independent From the 12th century (first and second Lateran thinkers by the Inquisition), Mr Galton attributes Councils) a great change took place in ecclesiastical much of the decadence of the country during the law. The marriage of priests was now declared to last three centuries. In France, where the most be not only sinful but invalid. It became hence promising lads of the village are successively picked forward difficult for any priest to justify his mar out by the parish priest for the bishop's seminary, riage on the plea that the prohibition of such the process of elimination must in the long run teli marriage was abrogated by custom, or not bind- upon the general character of the population. In ing under supposed exceptional circumstances. small Catholic communities, again, where the The clerical consorts became no longer wives but priestly vocation is held in high esteem by the concubines ; and, further, the priest who went educated classes, and where mixed marriages are throngh the marriage ceremony was held to commit discountenanced, a similar result cannot fail to a far greater crime than if he had contented himself

The controversial literature on the matter with simple fornication. Yet in spite of all this is abundant. The most complete treatment of the the law was to a large extent set at defiance. In subject, from the historical point of view,

will be many parts of Europe it was a common thing for found in Sacerdotal Celibacy in the Christiun benefices to pass from father to son.

Influential Church, by Henry C. Lea (Philadelphia, 1867). bishops obtained letters of legitimation for their | See also MONACHISM.


[ocr errors]
[blocks in formation]
[ocr errors][ocr errors]

Cell, a unit-mass of living matter, whether such as that of the nucleolus by Valentin (1836), rounded off by itself, as in the simplest plants or occurred in rapid succession during those years. animals and in the youngest stage of all organisms, Dujardin in 1835 described the sarcode or living or associated with other cells to form a higher matter of the Protozoan Foraminifera and of some unity. The great majority of the Protozoa and other cells, and thus emphasised, as Rösel von Protophyta are single cells, and all other organisms Rosenhof had done many years before (1755) in begin where the former leave off. From the double regard to the Proteus animalcule' or Ameba, the unity resulting from the fusion of two sex-cells the most important element to be considered in formhigher plants and animals develop by repeated ing a true conception of the cell. The importance division, and they may be therefore always resolved of his description, of which he was apparently himinto more or less close combinations of variously self unconscious, had for some time the same fate

as that of his predecessor of almost a century
before. Observations had in fact to accumulate
before any generalisation became possible. The
first definite steps towards a co-ordination of
results was probably that of Johannes Müller, who
in 1835 pointed out the resemblance between the
cells of the vertebrate notochord and the elements
observed in plants.

The cellular nature of the
Fig. 1.- Dividing Egg-cell (after Gegenbaur).

epidermis and the presence of nuclei therein was

next ascertained, and similar discoveries were made modified unit-masses. In most cases these in- in regard to several other tissues. Up to 1838 dividualities of the simplest order are minute, and there was in fact a period of research in which cells their separateness is not to be discerned with the were observed rather than understood. unaided eye, but there are many instances among Establishment of the Cell-theory.As early as the simplest plants and animals, as well as in the 1826 Turpin had maintained that plants were component elements of higher forms, where the formed by an agglomeration of cells

. Professor unit-masses are relatively giant-cells and quite M‘Kendrick well points out, what one would of visible without the use of the microscope. The course expect, that for some years before 1838 giant Ameba Pelomyxa, the common sun-ani. botanists were beginning generally to recognise malcule Actinospherium, the Alga Botrydium, the cellular composition and origin of plants. The and some of the cells (e.g. bast) of plants may be conclusion known as the “cell-theory was doubtnoted as illustrations of cells with considerable less vaguely present in many minds. Its definite dimensions. In the great majority of cases the statement was still awanting. In 1838, however, body of the cell includes a well-defined centre or Schleiden proved that a nucleated cell is the only nucleus; and the definition may therefore be original component of a plant embryo, and that the extended in the statement that a cell is a nucleated development of all tissues might be referred to such unit-mass of living matter or protoplasm.

cells. In the following year Schwann published I. History. In the article BIOLOGY it has been at Berlin his famous Microscopic Investigations on pointed out that a more and more penetrating the Accordance in the Structure and Growth of scrutiny alike of structure and of function led Plants and Animals (Trans. Sydenham Society, naturalists from organs to tissues, and from tissue 1847). In this classic work it was shown that all to cell.

Some of the steps in this gradually organisms, plants and animals alike, are made up deepening analysis deserve fuller record.

of cells, and spring from cells. In composition and Discovery of Cells.--In the latter half of the 17th in origin there is unity. The generalisation century the simple microscope afforded to Malpighi familiarly known as the cell-theory was thus and Leeuwenhoek, to Hooke and Grew, what clearly established, and though now a commonwas literally a vision of a new world. In place and postulate of histology, it may fairly be applying their rough and simple instruments to the described in Agassiz's words as the greatest disstudy of the structure of plants and animals they covery in the natural sciences in modern times. became pioneers in the investigation of the infinitely Following up the generalisations of Schwann and little. Leeuwenhoek (Phil

. Trans. 1674) seems to Schleiden, come a host of researches by which the have been the first to observe, what are now essential advance contained in the 'cell-theory' was familiar, single-celled organisms. In the 18th cen

more and more fully confirmed. Cells were not tury Swammerdam and others continued with much only observed, their import was recognised, enthusiasm to describe the minute intricacies

New Conception of the Cell.When the cell-theory which their new eyes' revealed ; Fontana (1784) was established, the general conception of the cell observed the kernel of the cell--the nucleus-and was far from being either accurate or complete. It some of the elements of the tissues; but the founda

was usually described as a vesicle closed by a solid tion of scientific histology was not laid until the membrane, containing a liquid in which float a appearance in 1801 of the Anatomie Générale of nucleus and granular bodies. Bichat. In this epoch-making work organs were general opinion that such cells originated within a resolved into their component tissues, and their structureless ground substance. In two ways functions were interpreted as the sum-total of the these notions were speedily corrected. On the one properties of their constituent elements. Such a

hand as regards the origin of cells, Prevost and conclusion was the utmost that could be reached Dumas (1824), Martin Barry (1838-9), Reichert with the appliances then at command.

(1840), Henle (1841), Kölliker (1846), Remak(1852), Early in this century, however, an improvement showed that in the case of the egg-cell, and in the in the appliances of observation furnished a fulcrum | growth of tissues, each new cell arose by division for a new advance. Fraunhofer discovered the from a predecessor.

This important conclusion principle of achromatic lenses (see LENS, MICRO was most firmly established by Goodsir in 1845, SCOPE); these were combined into the compound and Virchow in 1858, who proved that in all cases, microscope, and a new, era began. Fibres' and normal and pathological alike, cells arose from pre'globules,

* laminae,' nuclei,' and even 'cells' existing cells, a fact expressed in the axiom omnis were described.

In 1831 Robert Brown emphasised cellula e cellula. In the second place it gradually the normal presence of the nucleus discovered by recame apparent that too much importance hal Fontana, and made the first important advances in been attached to the cell-wall and too little to the the study of the vegetable cell. Isolated discoveries, I contained substance.

Referring details to the

[ocr errors]

It was also the

[blocks in formation]
[ocr errors][merged small]

article PROTOPLASM, we may note some of the (b) General Substance of the Cell.The cell is important steps. Dujardin (1835) described the much more than a mass of highly complex chemical sarcode' of Protozoa and other cells; Purkinje substance : it has an organised structure. (1) The (1839) emphasised the analogy, between the protoplasm or, living matter in the strictest sense protoplasm of the animal embryo and the is generally supposed to be an intimate mixture of cambium of plant-cells ; Von Mohi (1846) em complex and highly unstable chemical compounds. phasised in the clearest way the importance of the Inspection under a microscope of such cells as protoplasm in the vegetable cell; Ecker (1849) amæbæ, white blood-corpuscles, ova, simple algæ, compared the contractile substance of muscles with or such as are readily seen in thin slices of growing that of the amoeba ; Donders also referred the con plant-shoots, in root-hairs, and transparent parts, tractility from the cell-wall to the contained will at once furnish an impression of the general material; Cohn suspected that the ‘sarcode' of aspect of the substance of the cell. Not all that animal and the protoplasm of plant-cells must be one sees can of course deserve the name of proto'in the highest degree analogous substance ;' and plasm, for apart from definite inclosures like starch50 throughout another decade did botanists and grains and fat-globules, much of the remaining zoologists unite 'in laying stress rather on the slightly clouded substance is hardly to be strictly living matter than on the wall of the cell, and in called "protoplasm, but rather represents steps in hinting at the existence of one living substance as the ceaseless making and unmaking which form the physical basis alike of plants and animals. the fundamental rhythm of life. Keeping the This view found at length definite expression in definite inclosures and products for the moment 1861, when Max Schultze defined the modern con aside, we may briefly notice in general outline ception of the cell as a unit-mass of nucleated what has been with most conclusiveness observed protoplasın. Since then the protoplasmic move as to the structure of the general cell-substance or ment has dominated research, and we think not cytoplasm' as it is now frequently termed. All so much of the cell-containing protoplasm as of the observers agree that the structure is far removed protoplasm which constitutes and gives form to the from the homogeneous, though there is much difcell.

ference of opinion as to the nature of the hetero)II. Structure of the Cell. While it is impossible geneity. In a large number of cases at least the to isolate the static from the dynamic aspects of substance of the cell has been resolved into two the cell, it will be convenient to discuss the two distinct portions—the one an intricate network, separately, and to consider the cell at rest and knotted and interlaced in a manner baffling descripdead, apart from the cell active and alive. In tion ; the other a clear substance, filling up the other words, the form, structure, or morphology interstices or meshes of the living net. Leydiy, may be studied for literary clearness apart from the Frommann, and Heitzmann have been peculiarly functions, life, and physiology.

successful in unravelling this knotted structure in (a) General Form. The typical and primitive animal cells, and much the same has been recorded form of the cell is spherical. This is illustrated by by Strasburger and Schmitz as observable in some many of the simplest plants and animals which live plants. The reticulate structure is certainly more freely, and by young cells such as ova. But the doubtful in regard to vegetable cells, and even in typical form is in many, indeed in most cases, lost; some animal cells what some have described as a and the forms assumed are as diverse as the network others have deemed only a minutely internal and external conditions of life. The cell bubbled emulsion. may be irregular and protean, as in Amoebæ, white But besides the real substance of the cell there blood-corpuscles, and many young eggs;

are to be seen products of various kinds formed squeezed into rectangular shape, as in much of the from the living matter. The cell may be packed substance of a leaf; or flattened into thinness, as in with starch, or laden with fat, or expanded with the outer lining of the lips; or oval and pointed, as mucus ;

it may contain colouring matter in various in swiftly moving Infusorians and Bacteria ; or forms, as in the familiar chlorophyll bodies of many much branched, as in multipolar ganglion cells of plant-cells; its structure may include, as in some animals or the latex-containing cells of some plants. Protozoa, definitely formed fibrils or yet firmer forThe typical spherical and self-contained form is mations of chitin and the like; and again there are that which would naturally be assumed by a com

concretions of retained waste and reserve products, plex coherent substance situated in a medium sometimes in the form of crystals. Not to be overdifferent from itself. The other forms are responses looked either is the fine *dust-cloud' of minute to internal and external conditions. Under the granules which are seen suspended in the clearer heading Cell-cycle below it will be shown how the matrix, and which apparently represent aggregarelative activity and passivity of the cell naturally tions of diverse chemical substances formed in the expresses itself in such extremes as a long-drawn building up and breaking down of the protoplasm, out Infusorian and a rounded-off Gregarine, or in a As the outside of any mass is bound to be in differhighly nourished ovum and a mobile spermatozoon. ent conditions from the inside, it is natural to find Further

, cells, like entire animals, often show a the appearance of distinct physical and chemical tendency to become two-ended, to have poles very zones in the cell-substance. Thus in many Protozoa different from one another. Just as an animal may the outer portion, needlessly termed ectoplasm,' is have a highly nourished head and a scantily often denser and more refractive than the more nourished tail, so a cell may become distinctly fluid and internal stratum of the 'eudoplasm. Or bipolar in form. In other cases the cell is altogether this may go further, and we may have a sweatedplastic, expressing every impulse of internal change off

' limiting cuticle, or a definitely organised wall and every impact of external influence in some of cellulose in vegetable cells. The cuticle may modification of form. Or the state of nutrition of be further substantiated with secretions of horny, the living matter may cause alteration in the finty, limy, and other material. Even within adhesion of the substance all over, or in particular the cell a stratified structure may be frequently places

, and thus condition an outflowing, regular observed, and Berthold and others have recently or irregular, in given directions. Furthermore, ex emphasised the existence of such concentric layers, terual pressure and limitation of growth may each characterised by its own special set of the square off the cell into a parallelogram, or restrict posits. it to grow like a bast fibre in length alone and not Worthy of notice, too, are the various kinds of in breadth. In fact the conditions are most mani- bubbles or vacuoles which occur in the cell-sulfold, and the resultant forms likewise.

stance. These may be simply indefinite spaces,



[blocks in formation]



containing some liquid not protoplasm, and includ- and active nature. In accordance with the growth ing salts and other substances in solution. In many of the cell it may occupy a position distinctly Protozoa they are “food-vacuoles,' formed by the nearer one of the poles. Accumulations of fat or

mucus may push it passively to the side. Or it may actively change, in response to hidden forces of attraction between it and the surrounding proto plasm, in the case of some ova exhibiting a peculiar rotation, or else distinctly shifting its ground from the centre towards the periphery.

Structure.—In many cases, as Leydig especially has shown, the nucleus seems to lie in a nest of its

own, in a clear space within the surrounding cellFig. 2.

substance. Nor is it in many cases at least deA, Embryonic cells from growing point of a root; B, older cells finitely insulated from the surrounding protoplasm, becoming vacuolated. (After Sachs.)

but is moored to the latter by strands which have

intimate relations with both. As of the entire cell, bubbles of water engulfed along with the food so of the nucleus it must be said that in the great particles, round which the protoplasm, shrinking majority of cases it is very far from being homofrom contact, often forms a definite contour. In geneous. According to Hertwig, Schleicher, Schmitz, other cases they are more permanent, and represent Brass, and others, homogeneous nuclei may indeed minute reservoirs of secreted substance, cisterns of occur, but if they do they are rare, and it must by-products in the vital manufacture of the cell. always be remembered that the nucleus has its Finally they may be seats of special activity, where, history, and may be less complex at one time than perhaps, under the stimulus of irritant waste-pro- it is at another. To Flemming (1882) above all is ducts, the protoplasm exhibits spasmodic contrac- due the credit of having elucidated the complexity tions and expansions, and forms the so-called “con of the nucleus, and the labyrinthine structure to tractile vacuoles,' which in alternate dilatation and which he showed the clue, and to which Frommann bursting often seem to serve to remove fluid from (1867) had many years previously directed special the living matter to the exterior.

attention, has been studied and restudied by scores (c) Nucleus.-In the great majority of cells a of expert histologists during the last six years central body of definite composition and structure (1888). While their results disagree abundantly is present which appears to be essential to the life on minor points, two conclusions stand out clearly and reproduction of the unit-mass. In many cases -(1) that the nucleus has a structure like that of the nucleus is well concealed, but as more skilful the general cell, consisting of firmer framework staining has revealed its presence in many cells and of more fluid intermediate substance, and (2) which used to be described as non-nucleated, it is that apart from detailed difference there is throughrash to conclude too certainly as to its absence in out the world of cells a marvellous unity of strucany particular case. Thus some of the Monera, ture and process, in the nucleus in repose and in which were formerly defined as the simplest of the nucleus in action. simple animal organisms without even a nuclei, In the nucleus the following parts have to be dishave been shown to possess them, and the line of tinguished : (1) The readily stained firmer threaddivision separating Protozoa into Monera and work, (2) an intermediate clear substance filling Endoplastica has therefore been removed. Fur up the interstices, (3) definite and usually globular thermore, the researches of Gruber have shown that formations known as nucleoli, (4) various granules

, in some of the higher Protozoa (ciliated Infusorians) and (5) a limiting membrane or nuclear wall. where the nucleus seems entirely, absent, dex- These may be briefly touched upon in order. terous staining prove its diffused presence in (1) The Nuclear Framework (reticulum, trabecuthe form of numerous granules which take on the lar framework, &c.). -A mere statement of the characteristic nuclear dye. Yet in some cases, different descriptions given of this important part such as the young spores of some Protozoa, of the nucleus would carry us far beyond the limits the greatest care has not yet been successful in of this article. The most marked difference of proving the presence of the nucleus. In contrast opinion is this, that some describe the framework with these cases, many cells exist in which the as distinctly of the nature of a network, while nucleus is represented not by one, but by many others are as emphatic in calling it a much-coiled bodies--the so-called polynuclear state. A further band. A third party unite both views, and me reserve requires to be made, that it is to a large garding the nucleus as variable, describe a retiextent an hypothesis that all such definite central culum at one time and a coiled filament at another. inclosures should be slumped together under the Thus, according to Flemming, Pfitzner, Retzius, one title of nucleus. It is rather probable that in Leydig, Van Beneden, &c., the nuclear framework this, as in other organic structures, we have to do is typically a reticulum ; according to Strasburger

, with various degrees of development and definite Balbiani, and Korschelt, a twisted ribbon is the

only or most frequent form ; according to Brass In the form also of the nucleus numerous modi and Rabl, both types may equally occur. fications occur. In the majority of cases, indeed, complication has been emphasised by Zacharias, it is more or less spherical, but it may be elongated, Plitzner, Carnoy, and others—this

, namely, that curved, horseshoe-shaped, necklace-like, and even besides the readily stained threadwork noted above branched. In the young stages of some ova it is (the so-called chromatin), whether this be in the like the entire cell, somewhat plastic, and is pulled form of a reticulum (Pfitzner) or of a coiled ribbon in and out in amoboid movements. In special con (Carnoy), there exists another—not readily stained ditions, furthermore, the nucleus may exhibit -framework of achromatin. This had indeed been peculiar deformations. It is in fact a peculiarly recognised though not insisted on by the first series sensitive and all-important part of the cell, suffering of investigators. To sum up, it is now generally with it in degeneration, changing with it in growth allowed that the framework or threadwork of the and division.

nucleus may exist as a network or as a coil, and In position the nucleus is typically central, where that it is in a sense double, consisting of readily as the presiding genius of the cell it shares and stainable chromatin on the one hand, and unstainperhaps controls the general protoplasmic life. Butable achromatin on the other.

It need hardly be it frequently suffers displacement both of a passive added that as there is considerable diversity of


A further

[ocr errors]
[blocks in formation]


[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]

opinion as to whether given nuclei have a netted or from an aggregation of the threads and knots of
coiled framework, there is yet greater variety in the framework; (2) as a cuticle or capsule formed
the minuter description and figuring. According from the matrix or ground substance; (3) from a
to Flemming the network is quite disorderly, but combination of both these elements. Leydig has
Ranber, Leydig, and others have described distinct | shown that in a very wide series of animal cells

the membrane, such as it is, is penetrated by small
but definite pores. It is very important further
to remember that both in plants and animals the
cells are in a great number of cases connected with
one another by intercellular bridges of protoplasm,
and are in nowise to be thought of as closed bags.
The cell-wall of plants, which, be it again noted,
is a definite chemical substance, grows in extent
and thickness by an intricate organic process, in
the course of which new infinitesimal elements
form apparently as intercalations between the old.
The growth is in very many cases far from uni-
form; pits, ridges, and manifold kinds of sculptur-
ing thus appear, and give rise to numerous detailed

variations. The formation of new boundaries when
Fig. 3.—(After Carnoy):

a cell divides is a question of much difficulty; but

in plant, and apparently in some animal cells, the A, Cell and typical nucleus : &, slight membrane; b, radiating

formation of a protoplasmic network; C, wall of nucleus; d, plasma of

cellular plate’ is one of the last nucleus; e, nuclear coil.

events in the dividing process, B, Nucleus at rest, showing network.

III. Physiology of the Cell.—When the entire C, Nucleus before division, showing coiled filament.

organism is simply a cell, as in most of the Proto

zoa and Protophyta, all the vital processes which radial structure ; according to some the nuclear coil in higher forms have their seat in special sets of is endless, while others describe it as divided into | cells, known as tissues and organs, are of course portions; and when we descend to such subtleties | discharged by the unit-mass. Thus a unicellular of observation as the intimate structure of the organism like the Ameba takes in energy as food threadwork or the relations between chromatin in nutrition, works it up into living matter in and achromatin, the diversity is so great that it digestion and assimilation, and expends it again seems desirable here to leave such minuti un in contraction and locomotion. As in auy higher touched.

organism the oxygen required for the chemical .(2) The Intermediate Nuclear Substance. --Be- breaking up of the protoplasmic molecules, the sides the nuclear elements of definite form, what- air for the vital flame, is taken in by the absorpever that form may precisely be, all investigators tion known as respiration, and the waste carbonic describe an intermediate substance of variable acid gas is in an essentially similar way got rid consistence, usually semi-liquid, amorphous and of. Further, more solid 'ashes' of the vital comstructureless, but with fine granules. It is a clear bustion are formed in the Ameba and in other unstainable "plasma' filling up the chinks, but actively living, cells, and may pass out in excrenothing definite is known as to its composition. tion along with the refuse of unusable food(3) The nucleolus which lies within the nucleus material. The absence of a circulating fluid, of varies greatly in size and position, and more than one digestive glands, nerves, sense-organs, lungs, are very generally present. Flemming has defined kidneys, and the like, does not in any way them as 'portions of the nuclear substance, distinct restrict the vital functions of a unicellular organin structure from network and plasma, definitely ism. All goes on as usual, only with greater limited and smoothed, always rounded in outline, chemical complexity, since all the different prousually suspended in the network, but often inde cesses have but a unit-mass of protoplasm in pendent of it.' But when the minute structure which they occur. The physiology of independent and the relation of nucleoli to nuclear framework cells, instead of being very simple, must be very are inquired into, or the question of physiological complex, just because structure or differentiation rôle raised, very great diversity of opinion is found is all but absent. It is, however, possible to exto obtain. (4) Bodies different in appearance from press the manifold processes in a comparatively nucleoli may occur inside the nucleus, but of these simple way by remembering what Claude Bernard little is known. (5) The wall which bounds the was one of the first clearly to emphasise, that pucleus seems to be a true integral part of the vital processes must be really only twofoldlatter, but disappears at the beginning of division. building up and breaking down of living matter.

(d) The Cell-wall.-In the older conception of On the one hand the protoplasm or real living the cell

, which was practically that of a closed matter is being by a series of chemical processes bag, the wall of the cell figured very prominently. built up or constructed ; on the other hand, in But Nägeli showed (1845) that some vegetable activity it is breaking down or being destroyed. cells were destitute of walls, Leydig (1857) de

The income of food or energy is, at the expense fined the cell in respect to its substance, Schultze of the cellular organism, gradually raised into and others described naked Protozoa, and the more and more complex and unstable compounds, progress of the protoplasmic movement' led to until the genuine most complex and more unthe abandonment of the position that the wall was stable living matter itself is reached. On the a necessary or important part of the cell. In opposite side, with liberation of energy in the many cells, indeed, a limiting layer is very clearly form of work, this living matter breaks down present, and a sheath or cyst is especially charac into simpler and simpler compounds, until only teristic of passive cells.

Plant-cells are almost the work, the waste products, and heat remain as always distinguished by the possession of a limit the equivalent of the income of energy or food on ing wall, of definite chemical composition, consist

the other side of the life-equation. On the one ing of what is known as cellulose. An analogous hand there are constructive processes, on the other, wall occasionally occurs round animal cells. In destructive; chemical synthesis and chemical disthe latter, however, the membrane is usually a solution is another expression of the contrast; comparatively slight thing, and may arise (1) while the two sets of processes are in more modern

[merged small][ocr errors]
« PrécédentContinuer »