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The World's Greatest Books [Volumes 1-15, 17-20]
- Автор: Gutenberg
- Год: 1910
- Язык: английский
- Жанр: Культурология
Электронная книга - «The World's Greatest Books [Volumes 1-15, 17-20]». Краткое содержание книги:
The World's Greatest Books — Volume 01 — Fiction от Неизвестный
The World's Greatest Books — Volume 02 — Fiction от Неизвестный
The World's Greatest Books — Volume 03 — Fiction от Неизвестный
The World's Greatest Books — Volume 04 — Fiction от Неизвестный
The World's Greatest Books — Volume 05 — Fiction от Неизвестный
The World's Greatest Books — Volume 06 — Fiction от Неизвестный
The World's Greatest Books — Volume 07 — Fiction от Неизвестный
The World's Greatest Books — Volume 08 — Fiction от Неизвестный
The World's Greatest Books — Volume 09 — Lives and Letters от Неизвестный
The World's Greatest Books — Volume 10 — Lives and Letters от Неизвестный
The World's Greatest Books — Volume 11 — Ancient and Mediæval History от Неизвестный
The World's Greatest Books — Volume 12 — Modern History от Неизвестный
The World's Greatest Books — Volume 13 — Religion and Philosophy от Неизвестный
The World's Greatest Books — Volume 14 — Philosophy and Economics от Неизвестный
The World's Greatest Books — Volume 15 — Science от Неизвестный
The World's Greatest Books — Volume 17 — Poetry and Drama от Неизвестный
The world's greatest books от Mee, Arthur, 1875-1943, joint editor & Hammerton, John Alexander, Sir, 1871-1949, joint editor & McClure, S. S. (Samuel Sidney), 1857-1949, joint editor
The World's Greatest Books — Volume 19 — Travel and Adventure от Неизвестный
The World's Greatest Books — Volume 20 — Miscellaneous Literature and Index от Неизвестный
The second class 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 analogous 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 striæ. 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 classification, 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 quantities. The muscular elements of the arteries have the most important influence upon the quantity of the blood distributed, and their elastic elements ensure an equable stream; but it is chiefly the simple homogeneous 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 dyscrasiæ; 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 dyscrasiæ 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 leukæmia, 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 pyæmia is meant pus corpuscles in the blood. But most cases of so-called pyæmia 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 pyæmia. 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.
Chlorosis is a condition in which there is a diminution of the cellular elements of the blood, due probably to their deficient formation in the spleen and lymphatic glands.
The Vital Processes and Their Relation to Disease. Inflammation
The study of the histology of the nervous system shows that in all parts of the body a splitting up into a number of small centres takes place, and that nowhere does a single central point susceptible of anatomical demonstration exist from which the operations of the body are directed. We find in the nervous systems definite little cells which serve as centres of motion, but we do not find any single ganglion cell in which alone all movement in the end originates. The most various individual motor apparatuses are connected with the most various individual motor ganglion cells. Sensations are certainly collected in definite ganglion cells. Still, among them, too, we do not find any single ganglion cell which can be in any way designated the centre of all sensation, but we again meet with a great number of very minute centres. All the operations which have their source in the nervous system, and there certainly are a very great number of them, do not allow us to recognise a unity anywhere else than in our own consciousness. An anatomical or physiological unity has at least as yet been nowhere demonstrated.
When we talk of life we mean vital activity. Now, every vital action supposes an excitation or irritation. The irritability of the part is the criterion by which we judge whether it be alive or not. Our notion of the death of a part is based upon nothing more or less than this—that we can no longer detect any irritability in it. If we now proceed with our analysis of what is to be included in the notion of excitability, we at once discover, that the different actions which can be provoked by the influence of any external agency are essentially of three kinds. The result of an excitation or irritation may, according to circumstances, be either a merely functional process, or a more or less increased nutrition of the part, or a formative process giving rise to a greater or less number of new elements. These differences manifest themselves more or less distinctly according as the particular tissues are more or less capable of responding to the one or other kinds of excitation. It certainly cannot be denied that the processes may not be distinctly defined, and that between the nutritive and formative processes, and also between the functional and nutritive ones there are transitional stages; still, when they are typically performed, there is a very marked difference between them, and considerable differences in the internal changes undergone by the excited parts.