Organ (biology)

“ That among animals physiological development is furthered by the multiplication of effects, we have lately seen proved by the many changes in other organs, which the growth or modification of each excreting and secreting organ initiates. ”

“ In the first place it is assumed that the fragment of matter out of which each organism arises consists of two portions—one of them, the germ-plasm, reserved within the generative organ of the incipient individual, representing in its components the structure of the species, and gives origin to the germs of future individuals ”

“ While the quantity of blood supplied to other organs is affected, its quality also is in some cases affected. Each organ, or at any rate each class of organs, has special nutrition—abstracts from the blood a proportion of ingredients different from that abstracted by other organs or classes of organs. ”

“ As the body is composed of individual organs, and each organ of separate tissues, so each tissue is made up of minute cells. Each cell is a little world by itself, too small to be seen by the naked eye, but open to the microscope. It has its own form and constitution as much as a special organ in the body. It absorbs from the blood such food as suits its purposes. Moreover, the number of cells in an organ is as constant as the number of organs. As the organs expand with the growth of the body, so the cells of each tissue enlarge, but shrink again with age and the decline of life. ”

“ Among certain lower and microscopic organisms, such for instance as the Rotifera, we are still more palpably struck by the small number of cells which go to constitute a usually complex organ, such as kidney, stomach, ovary, etc. ”

“ If regenera­tion takes place in pieces which take up no food the newly formed organs must originate from material absorbed from cells of the animal which are hydrolyzed and whose material serves as food for those cells which grow. Very often this process of diges­tion takes place without loss of the total form of the organ and is overlooked by the pure morphologists. ”

“ The main systems of organs are, in order of importance, the nervous and muscular, the digestive, the circulatory, and the respiratory. Each organ or system of organs may have many forms. If any form of any organ could exist in combination with any form of all the others there would be an enormous number of combinations theoretically possible. But these combinations do not all exist in Nature, for organs are not merely assembled (rapprochés) , but act upon one another, and act all together for a common end. ”

“ Thus everything we can see in animals is adaptation, whether of to-day, or of yesterday, or of ages long gone by; every kind of cell, whether glandular, muscular, nervous, epidermic, or skeletal, is adapted to absolutely definite and specific functions, and every organ which is composed of these different kinds of cells contains them in the proper proportions, and in the particular arrangement which best serves the function of the organ ”

“ No animal organ with a function of essential importance presents such extraordinary modifications in related species and genera. In the heart, brain, and other organs there is one shape, position, and condition of greatest efficiency, and throughout the lower forms we find a steady advance towards this condition. Great variation, on the other hand, usually indicates that the organ is of little functional importance, or that it has lost its original function. Such we conceive to be the case with the air-bladder. ”

“ The knowledge that digestion is the means by which unsuitable products are prevented from passing into the blood and the cells of the body is of the greatest importance for our comprehension of the whole metabolism of the animal organism. Thus, to a certain extent, we may look upon the animal organism as a whole in itself. All the cells of the body have a common architecture, which is bequeathed from generation to generation by means of the sexual cells. The cells which combine into an organ have, besides that, a structure specific for the organ. ”

“ If you should prick your finger and extract a drop of your own blood, and examine it under a microscope, you would make the fascinating discovery that it is the home of living creatures, each having a separate and independent existence of its own. In a single ounce of blood there are more of these organ [Pg 22] isms than there are human beings upon the face of the globe. These organisms are of many kinds, but they divide themselves into two main groups, known as the red corpuscles and the white. ”

“ If our ideas concerning the structure of the particular cells of an organ, and the dependence of its functions on this peculiarity, prove correct, then it follows that, as we have already emphasized, each kind of cell must have at its disposal units of its own kind. We may then speak of substances that are "in harmony with" an organ, or even more precisely, "with the cells" ”

“ Let us not, however, exaggerate this independence of the textures of the organs in diseases, lest experience should contradict us. We shall see that the cellular system is oftentimes a medium of communication, not only from one texture to another in the same organ, but from one organ to a neighbouring one. ”

“ An organ may be composed of several tissues. Thus the heart has contractile tissue in its muscular walls, epithelial tissue lining its cavities, and skeletal tissue forming its framework. Still, notwithstanding their aggregation [21] into tissues and organs, it remains true that the body of one of the higher animals is composed of cells, together with certain cell-products, horny, calcareous, or other. The simplest animals, called protozoa, are, however, unicellular, each organism being constituted by a single cell. ”

“ When we reflect on the part played in the body by the blood, we readily see that a correct idea of how it carries nourishment to the tissues, and how it brings away from them the products of disintegrated protoplasm is of prime importance in physiology. It is the point from which spring all other ideas of the action of tissues, and until this was known the fine analysis of vital processes could not be made. The true idea of respiration, of the secretion by glands, the chemical changes in the tissues, in fact, of all the general activities of the body, hinge upon this conception. ”

“ This distinction is diagnostic but not perfectly characteristic; that is, we may safely classify as an animal any organism in which we find a definite, sharply-limited body, and complicated internal viscera, such as a digestive tract, respiratory organs, blood-vessels, internal reproductive organs, and a nervous system and sense-organs; while we may, with almost equal safety, refer to the vegetable kingdom an organism in which the nervous, sensory, and circulating organs are wanting, and the processes of absorption and respiration take place through the outer surface. ”

“ It is thought of as a very minute corpuscle of living matter. Thus there are determinants of hairs and scales, pieces of skin, pits, marks, &c. But every determined organ, or part, or “independent region,” is itself in its turn an “organism,” is indeed a system of an infinite number of interrelated component parts, and each of these again is another, down to the individual cells. And each cell is an “organism” in itself, and so on into infinity. Is all this represented in the determinants? ”

“ Throughout life, millions of these cells retain their primary characters, and constitute the white corpuscles of blood, "phagocytes," and connective tissue corpuscles; others again, engage in the formation of material round themselves, and lie, in such cases, as gristle and bone, embedded in the substance they have formed; others again, undergo great changes in form and internal structure, and become permanently modified into, for instance, nerve fibres and muscle substance. ”

“ From the common nutritive fluid, the blood, protoplasm is formed in all the tissues of the body, and we must look upon the characteristic elements and products of these tissues as the result of its destructive metabolism. In each organ of the body the protoplasm appears to have special endowments adapted to their specific functions, but these diverse activities are correlated to serve a common purpose in the life of the individual. ”

“ No other animal gives nourishment to its young in such fashion; all mammals do. What is the origin of the habit? How did the organ arise?
A part of an animal's body that has the power to gather material from the blood and pour it out in the shape of fluid is known as a gland. Sometimes a whole organ does nothing else. Sometimes small glands are scattered through, or over, the surface of another organ. There are two kinds of glands in the skin of the mammal. The best known and most frequently thought of are those which pour out the perspiration. ”

“ Organs and Functions Common to All Animals.—The same general functions performed by a single cell are performed by a [Pg 181] many-celled animal. But in the many-celled animals the various functions of the single cell are taken up by the organs. In a complex organism, like man, the organs and the functions they perform may be briefly given as follows:—
(1) The organs of food taking: food may be taken in by individual cells, as those lining the pores of the sponge, or definite parts of a food tube may be set apart for this purpose, as the mouth and parts which place food in the mouth. ”

“ On this analogy, many have suggested that every organ in the body—we must go further, and say that every marked feature in every organ in the body—is represented in the germ by a seed which can grow, under favourable circumstances, into just such another organ or feature of an organ. ”

“ The next step was based on the observation that organs are composed of simpler parts called tissues. Often several different kinds of tissue will unite into one organ; for example, the heart is not all muscle but connective tissue and nerves enter into it; the walls of the stomach also contain glands, muscles, nerves, connective tissue, etc., all united to form the one organ—the stomach. The leaf of a plant is not all one kind of tissue, but several different kinds enter into it. We are thus approaching step by step the finer structure of living beings. ”

“ The similarity of the texture of the brain to that of the pancreas, and some other glands of the body, has induced the inquirers into this subject to believe, that a fluid, perhaps much more subtile than the electric aura, is separated from the blood by that organ for the purposes of motion and sensation. ”

“ The internal cellular texture of each organ has but little of the vital character which distinguishes that organ; it preserves almost all its general properties; it is, in the structure of different parts, the medium which unites without resembling them. ”

“ All animals therefore, I contend, have a similar cause of their organization, originating from a single living filament, endued indeed with different kinds of irritabilities and sensibilities, or of animal appetencies; which exist in every gland, and in every moving organ of the body, and are as essential to living organization as chemical affinities are to certain combinations of inanimate matter. ”

“ Out of the blood all of the tissues are wrought, each in its kind, and every tissue is a kind of its own, and there are kinds of kinds, so that the animal organism is a chemical laboratory engaged during the existence of the animal in building up more complex substances and tearing them down into more specialized substances, and this is metabolism, or zoochemistry. ”

“ We have, in the skeleton, a complicated apparatus of parts hinged and movable upon one another; the agent moving these parts is the same agent that we find in the heart walls propelling the blood through the circulation, in the alimentary canal squeezing the food along its course, and universally in the body where motion occurs, except in the case of the creeping phagocytes, and the ciliary waving of ciliated epithelium. This agent is muscle. We have, in muscular tissue, a very wide departure from the structure of the primordial cell ”

“ For example, a group of cells which would behave towards all stimuli impartially were they independent unicellular organisms become, as an organ in a multicellular organism, amenable only to mechanical or only to chemical stimuli,—become, that is to say, an organ of touch and of hearing, or an organ of taste and also of smell; until, finally, when differentiation is sufficiently advanced, the group ends by becoming exclusively the organ of one specified sense, touch or hearing in the one case, taste or smell in the other. ”

“ All living bodies are made up of tissues. There is no part, no organ, however soft and yielding, or hard and resisting, which has not this peculiarity of structure. The bones of animals, as well as their flesh and fat, are composed of tissues, and all alike made up of cells. When viewed under a microscope, each cell is seen to consist of three distinct parts, a nucleolus, or dark spot, in the center of the cell, around which lies a mass of granules, called the nucleus ”

“ The word “organ” signifies some part or parts of the body that have a particular use or function: thus, muscles are organs of motion, and nerves of sensation; the eye is the organ of sight, and the heart and blood vessels are the organs for circulating the blood. Now, any structure is said to be organized, or to have organization, that possesses the properties which distinguish a living body from one that never had life. Therefore we speak of the organic world as distinguished from the inorganic; the former includes plants and animals, the latter minerals, etc. ”