The derivative origin of species, then, being at present the most admissible one, and the retrospective survey of such species showing convergence, as time recedes, to more simplified or generalised organisations, the result to which the suggested train of thought inevitably leads is very a.n.a.logous in each instance. If to kosmos or the mundane system have been allotted powers equivalent to the development of the several grades of life, may not the demonstrated series of conversions of force have also included that into the vital form?

In the last century, physiologists were divided as to the principle guiding the work of organic development.

The "evolutionists" contended that the new being preexisted in a complete state of formation, needing only to be vivified by impregnation in order to commence the series of expansions or disencasings, culminating in the independent individual.

The "epigenesists" held that both the germ and its subsequent organs were built up of juxtaposed molecules according to the operation of a developmental force, or "nisus formations."

At the present day the question may seem hardly worth the paper on which it is referred to. Nevertheless, "pre-existence of germs" and evolution are logically inseparable from the idea of species by primary miraculously-created individuals. Cuvier, therefore, maintained both as firmly as did Haller. In the debates of 1830 I remained the thrall of that dogma in regard to the origin of single-celled organisms whether in or out of body. Every result of formfaction, I believed, with most physiologists, to be the genetic outcome of a pre-existing "cell." The first was due to miraculous interposition and suspension of ordinary laws; it contained potentially all future possible cells.

Cell-development exemplified evolution of pre-existing germs, the progeny of the primary cell. They progagated themselves by self-division, or by "proliferation" of minutes granules or atoms, which, when properly nourished, again multiplied by self-division, and grew to the likeness of the parent cells.

It seems to me more consistent with the present phase of dynamical science and the observed graduations of living things to suppose the sarcode or the "protogenal" jelly-speck should be formable through the concurrence of conditions favouring such combination of their elements, and involving a change of force productive of their contractions and extensions, molecular attractions, and repulsions--and the sarcode has so become, from the period when its irrelative repet.i.tions resulted in the vast indefinite ma.s.ses of the "eozoon," exemplifying the earliest process of "formification" or organic crystallisation--than that all existing sarcodes or "protogenes" are the result of genetic descent from a germ or cell due to a primary act of miraculous interposition.

I prefer, while indulging in such speculations, to consider the various daily nomogeneously developed forms of protozoal or protistal jellies, sarcodes, and single-celled organisms, to have been as many roots from which the higher grades have ramified than that the origin of the whole organic creation is to be referred, as the Egyptian priests did that of the universe, to a single egg.

Amber or steel, when magnetised, seem to exercise "selection"; they do not attract all substances alike. A speck of protogenal jelly or sarcode, if alive, shows a.n.a.logous relations to certain substances; but the soft yielding tissue allows the part next the attractive matter to move thereto, and then, by retraction, to draw such matter into the sarcodal ma.s.s, which overspreads, dissolves, and a.s.similates it. The term "living" in the one case is correlative with the term "magnetic" in the other. A man perceives ripe fruit; he stretches out his hand, plucks, masticates, swallows, and digests it.

The question then arises whether the difference between such series of actions in the man and the attractive and a.s.similative movement of the amaeba be greater or less than the difference between these acts of the amaeba and the attracting and retaining acts of the magnet.

The question, I think, may be put with some confidence as to the quality of the ultimate reply whether the amaebal phenomena are so much more different, or so essentially different, from the magnetic phenomena than they are from the mammalian phenomena, as to necessitate the invocation of a special miracle for their manifestation. It is a.n.a.logically conceivable that the same cause which has endowed His world with power convertible into magnetic, electric, thermotic and other forms or modes of force, has also added the conditions of conversion into the vital force.

From protozoa or protista to plants and animals the graduation is closer than from magnetised iron to vitalised sarcode. From reflex acts of the nervous system animals rise to sentient and volitional ones. And with the ascent are a.s.sociated brain-cells progressively increasing in size and complexity. Thought relates to the "brain" of man as does electricity to the nervous "battery" of the torpedo; both are forms of force and the results of action of their respective organs.

Each sensation affects a cerebral fibre, and, in so affecting it, gives it the faculty of repeating the action, wherein memory consists and sensation in a dream.

If the hypothesis of an abstract ent.i.ty produces psychological phenomena by playing upon the brain as a musician upon his instrument be rejected, and these phenomena be held to be the result of cerebral actions, an objection is made that the latter view is "materialistic" and adverse to the notion of an independent, indivisible, "immaterial," mental principle or soul.

But in the endeavour to comprehend clearly and explain the functions of the combination of forces called "brain," the physiologist is hindered and troubled by the views of the nature of those cerebral forces which the needs of dogmatic theology have imposed on mankind. How long physiologists would have entertained the notion of a "life," or "vital principle," as a distinct ent.i.ty if freed from this baneful influence may be questioned; but it can be truly affirmed that physiology has now established and does accept the truth of that statement of Locke--"the life, whether of a material or immaterial substance, is not the substance itself, but an affection of it."

RUDOLF VIRCHOW

Cellular Pathology

Rudolf Virchow, the son of a small farmer and shopkeeper, was born at Schivelbein, in Pomerania, on October 13, 1821. He graduated in medicine at Berlin, and was appointed lecturer at the University, but his political enthusiasm brought him into disfavour. In 1849 he was removed to Wurzburg, where he was made professor of pathology, but in 1856 he returned to Berlin as Professor and Director of the Pathological Inst.i.tute, and there acquired world-wide fame. His celebrated work, "Cellular Pathology as based on Histology,"

published in 1856, marks a distinct epoch in the science. Virchow established what Lord Lister describes as "the true and fertile doctrine that every morbid structure consists of cells which have been derived from pre-existing cells as a progeny." Virchow was not only distinguished as a pathologist, he also gained considerable fame as an archaeologist and anthropologist. During the wars of 1866 and 1870-71, he equipped and drilled hospital corps and ambulance squads, and superintended hospital trains and the Berlin military hospital. War over, he directed his attention to sanitation and the sewage problems of Berlin. Virchow was a voluminous author on a variety of subjects, perhaps his most well-known works being "Famine Fever" and "Freedom of Science." He died on September 5, 1902.

_The Cell and the Tissues_

The chief point in the application of Histology to Pathology is to obtain recognition of the fact that the cell is really the ultimate morphological element in which there is any manifestation of life.

In certain respects animal cells differ from vegetable cells; but in essentials they are the same; both consist of matter of a nitrogenous nature.

When we examine a simple cell, we find we can distinguish morphological parts. In the first place, we find in the cell a round or oval body known as the nucleus. Occasionally the nucleus is stallate or angular; but as a rule, so long as cells have vital power, the nucleus maintains a nearly constant round or oval shape. The nucleus in its turn, in completely developed cells, very constantly encloses another structure within itself--the so-called nucleolus. With regard to the question of vital form, it cannot be said of the nucleolus that it appears to be an absolute essential, and in a considerable number of young cells it has as yet escaped detection. On the other hand, we regularly meet with it in fully-developed, older forms, and it therefore seems to mark a higher degree of development in the cell.

According to the view which was put forward in the first instance by Schleiden, and accepted by Schwann, the connection between the three co-existent cell-const.i.tuents was long thought to be of this nature: that the nucleolus was the first to show itself in the development of tissues, by separating out of a formative fluid (blastema, cyto-blastema), that it quickly attained a certain size, that then fine granules were precipitated out of the blastema and settled around it, and that about these there condensed a membrane. In this way a nucleus was formed about which new matter gradually gathered, and in due time produced a little membrane. This theory of the formation of the cell is designated the theory of free cell formation--a theory which has been now almost entirely abandoned.

It is highly probable that the nucleus plays an extremely important part within the cell--a part less connected with the function and specific office of the cell, than with its maintenance and multiplication as a living part. The specific (animal) function is most distinctly manifested in muscles, nerves, and gland cells, the peculiar actions of which--contraction, sensation, and secretion--appear to be connected in no direct manner with the nuclei. But the permanency of the cell as an element seems to depend on nucleus, for all cells which lose their nuclei quickly die, and break up, and disappear.

Every organism, whether vegetable or animal, must be regarded as a progressive total, made up of a larger or smaller number of similar or dissimilar cells. Just as a tree const.i.tutes a ma.s.s arranged in a definite manner in which, in every single part, in the leaves as in the root, in the trunk as in the blossom, cells are discovered to be the ultimate elements, so it is with the forms of animal life. Every animal presents itself as a sum of vital unities, every one of which manifests all the characteristics of life. The characteristics and unity of life cannot be limited to any one particular spot in an organism (for instance, to the brain of a man) but are to be found only in the definite, constantly recurring structure, which every individual element displays. A so-called individual always represents an arrangement of a social kind, in which a number of individual existences are mutually dependent, but in such a way that every element has its own special action, and even though it derive its stimulus to activity from other parts, yet alone affects the actual performance of its duties.

Between cells there is a greater or less amount of a h.o.m.ogeneous substance--the _intercellular substance_. According to Schwann, the intercellular substance was cyto-blastema destined for the development of new cells; I believe this is not so, I believe that the intercellular substance is dependent in a certain definite manner upon the cells, and that certain parts of it belong to one cell and parts to another.

At various times, fibres, globules, and elementary granules, have been regarded as histological starting-points. Now, however, we have established the general principle that no development of any kind begins _de novo_ and that as spontaneous generation is impossible in the case of entire organisms, so also it is impossible in the case of individual parts. No cell can build itself up out of non-cellular material. Where a cell arises, there a cell must have previously existed (omnis cellula e cellula), just as an animal can spring only from an animal, and a plant only from a plant. No developed tissues can be traced back to anything but a cell.

If we wish to cla.s.sify tissues, a very simple division offers itself. We have (a) tissues which consist exclusively of cells, where cell lies close to cell. (b) Tissues in which the cells are separated by a certain amount of intercellular substance. (c) Tissues of a high or peculiar type, such as the nervous and muscular systems and vessels. An example of the first cla.s.s is seen in the _epithelial_ tissues. In these, cell lies close to cell, with nothing between.

The second cla.s.s is exemplified in the _connective_ tissues--tissues composed of intercellular substance in which at certain intervals cells lie embedded.

Muscles, nerves, and vessels form a somewhat heterogeneous group. The idea suggests itself that we have in all three structures to deal with real tubes filled with more or less movable contents. This view is, however, inadequate, since we cannot regard the blood as a.n.a.logous to the medullary substance of the nerve, or contractile substance of a muscular fasciculus.

The elements of muscle have generally been regarded as the most simple.

If we examine an ordinary red muscle, we find it to be composed of a number of cylindrical fibres, marked with transverse and longitudinal striae. If, now, we add acetic acid, we discover also tolerably large nuclei with nucleoli. Thus we obtain an appearance like an elongated cell, and there is a tendency to regard the primitive fasciculus as having sprung from a single cell. To this view I am much inclined.

Pathological tissues arise from normal tissues; and there is no form of morbid growth which cannot in its elements be traced back to some model which had previously maintained an independent existence in the economy.

A cla.s.sification, also, of pathological growths may be made on exactly the same plan as that which we have suggested in the case of the normal tissues.

_Nutrition, Blood, and Lymph. Pus_

Nutritive material is carried to the tissues by the blood; but the material is accepted by the tissues only in accordance with their requirements for the moment, and is conveyed to the individual districts in suitable quant.i.ties. The muscular elements of the arteries have the most important influence upon the quant.i.ty of the blood distributed, and their elastic elements ensure an equable stream; but it is chiefly the simple h.o.m.ogeneous membrane of the capillaries that influences the permeation of the fluids. Not all the peculiarities, however, in the interchange of nutritive material are to be attributed to the capillary wall, for no doubt there are chemical affinities which enable certain parts specially to attract certain substances from the blood. We know, for example, that a number of substances are introduced into the body which have special affinities for the nerve tissues, and that certain materials are excreted by certain organs. We are therefore compelled to consider the individual elements as active agents of the attraction. If the living element be altered by disease, then it loses its power of specific attraction.

I do not regard the blood as the cause of chronic dyscrasiae; for I do not regard the blood as a permanent tissue independently regenerating and propagating itself, but as a fluid in a state of constant dependence upon other parts. I consider that every dyscrasia _is dependent upon a permanent supply of noxious ingredients from certain sources_. As a continual ingestion of injurious food is capable of vitiating the blood, in like manner persistent disease in a definite organ is able to furnish the blood with a continual supply of morbid materials.

The essential point, therefore, is to search for the _local sources_ of the different dyscrasiae which cause disorders of the blood, for every permanent change which takes place in the condition of the circulating juices must be derived from definite organs or tissues.

The blood contains certain morphological elements. It contains a substance, _fibrine_, which appears as fibrillac when the blood clots, and red and colourless blood corpuscles.

The red blood corpuscles contain no nuclei except at certain periods of the development of the embyro. They are lighter or darker red according to the oxygen they contain. When treated with concentrated fluids they shrivel; when treated with diluted fluids they swell. They are rather coin-shaped, and when a drop of blood is quiet they are usually found aggregated in rows, like rouleaux of money.

The colourless corpuscles are much less numerous than the red corpuscles--only one to 300--but they are larger, and contain nuclei.

When blood coagulates the white corpuscles sink more slowly and appear as a lighter coloured layer on the top of the clot.

Pus cells are very like colourless corpuscles, and the relation between the two has been much debated. A pus cell can be distinguished from a colourless blood cell only by its mode of origin. If it have an origin external to the blood, it must be pus; if it originate in the blood, it must be considered to be a blood cell.

In the early stages of its development, a white blood corpuscle is seen to modify by division; but in fully-developed blood such division is never seen. It is probable that colourless white corpuscles are given to the adult blood by the lymphatic glands. Every irritation of a part which is freely connected with lymphatic glands increases the number of colourless cells in the blood. Any excessive increase from this source I have designated _leucocytosis_.

In the first months of the embryo the red cell multiplies by division.

In adult life the mode of its multiplication is unknown. They, also, are probably formed in the lymphatic glands and spleen.

In a disease I have named _leukaemia_, the colourless blood cells increase in number enormously. In such cases there is always disease of the spleen, and very often of the lymphatic glands.

These facts can hardly, I think, be interpreted in any other manner than by supposing that the spleen and lymphatic glands are intimately concerned in the production of the formed elements of the blood.

By _pyaemia_ is meant pus corpuscles in the blood. But most cases of so-called pyaemia are really cases in which there is an increase of white blood corpuscles, and it is doubtful whether such a condition as pus in the blood does ever occur. In the extremely rare cases, in which pus breaks through into the veins, purulent ingredients may, without doubt, be conveyed into the blood, but in such cases the introduction of pus occurs for the most part but once, and there is no persistent pyaemia.

Even when clots in veins break down and form matter like pus, it will be found that the matter is not really pus, and contains no pus cells.