Biological structure

“ At present, every individual animal or plant commences its existence as an organism of extremely simple anatomical structure; and it acquires all the complexity it ultimately possesses by gradual differentiation into parts of various structure and function. ”

“ Higher in the scale of animal life the forms will be found still more and more complex, with ever-increasing differentiation of the cells, with the combination of the differentiated cells into distinct organs, and the co-ordination of organs into systems of organs up to the extreme shown by the birds and mammals. And hand in hand with this increasing complexity of structure goes ever-increasing complexity or specialization of function. ”

“ Everywhere the peculiar form of the organism and its structures, internal and external, is directly related to the special physiological functions which the organism or organ has to execute. This intimate connection of structure and function, or of the instrument and the work done by it, is seen in the science of evolution and all its parts. ”

“ We have consequently to regard this proclivity of the physiological units, as producing, during the development of any organism, a combination of internal forces that expend themselves in working out a structure in equilibrium with the forces to which ancestral organisms were exposed; but not in equilibrium with the forces to which the existing organism is exposed, if the environment has been changed. ”

“ A third characteristic of undisturbed physiological evolution is this: the developed organs, when their evolution is complete, and indeed during their development, present a typical uniformity of structure; that is to say, organisms whose development has been perfectly natural, provided they are of the same age, sex, species, etc., are alike; and the several organs of different individuals present a uniform standard of size, shape, and functional power, any slight existing differences being so inappreciable as to evade ordinary methods of observation. ”

“ For though we come perilously near to it when we contemplate the lowest orders of magnitude to which life has been attributed, yet in the case of the ordinary cell, or ordinary egg or germ which is going to develop into a complex organism, if we have no reason to assume or to believe that it comprises an intricate “mechanism,” we may be quite sure, both on direct and indirect evidence, that, like the powder in our rocket, it is very heterogeneous in its structure. ”

“ There is an ensemble of vital phenomena presented by each organism in the course of its growth, development, and decay; and there is an ensemble of vital phenomena presented by the organic world as a whole. Neither of these can be properly dealt with apart from the other. But the last of them may be separately treated more conveniently than the first. What interpretation we put on the facts of structure and function in each living body, depends entirely on our conception of the mode in which living bodies in general have originated. ”

“ Hence the invariable character of the germ-cells. In bone-formation, it is clearly shown that special structure begins very early,—in the cell, namely; but it is preserved only where it is aided by the necessary action and reaction. Autonomic in itself, life submits itself to the general laws of evolution. [67] As the direction of motion is determined for whole groups of cells by the direction of the motion of the protoplasm in the single cells, so organic function is determined by the grouping of the irritable, contractile, sensible cells. ”

“ Premising, then, that the ordinary idea of mechanical action must be greatly expanded, let us enter upon the question at issue—the sufficiency of the hypothesis that the structure of each organism is determined by the polarities of the special molecules, or physiological units, peculiar to it as a species, which necessitate tendencies towards special arrangements. ”

“ As the individual develops in the process of growth each organ goes as it were straight to its final form and structure without metamorphosis or especial alterations by the way. When this type of development occurs, the organism belongs to a type which is primitively simple. But there are other forms which in their adult state appear feeble or simple, in which are found elements of organs of high complexity. ”

“ Apparently each physiological unit, while having in a manner the whole organism as the structure which, along with the rest, it tends to form, has also an aptitude to take part in forming any local structure, and to assume its place in that structure under the influence of adjacent physiological units. ”

“ Thus Part I. deals with organic matter and its activity or metabolism, the action and reaction between organisms and their environment, the correspondence between organisms and their circumstances, and similar general data. Part II. states the big inductions regarding growth, development, adaptation, heredity, variation, and so on. Part III. deals with the arguments suggestive of organic evolution and with the factors in the process. Part IV. is a detailed interpretation of the evolution of organic structure, and Part V. an analogous interpretation of the evolution of functions. ”

“ In the next place, the general principles of biology hold true for the structure and physiology of the human species as they do for all other living things. A human body is composed of eight systems of organs, whose functions are identical with the eight vital tasks of every other animal. All these organs are made up of cells as ultimate vital units, and the materials of which human cells are composed belong to the class of substances called protoplasm. ”

“ Q. What is the peculiarity of living matter as to the power of nutrition and growth? A. The non-living increases in size by external additions; but bioplasm selects appropriate material from its food, or pabulum, changes the chemical relations of this material, and appropriates it to its own structure in such a way that it grows from within.
14. Q. What is the peculiarity of bioplasm as to reproduction A. Bioplasm can generate or reproduce its own kind of living matter.
15. Q. What power has a living thing to preserve its own identity? ”

“ We now come to consider some ©f the functions of organic life, premising that in all organs where these vital operations are car- ried on, we find a true cellular structure retained. Beginning with absorption and assimilation, we fiad these processes varying, ac- cording to the rank of the animal or plant, in the respective kingdoms, but still agreeing in the constant cellular agency. ”

“ Moreover, it is a demonstrable impossibility to explain the origin of just those organs and members in the structure of organisms which are systematically the most significant and functionally the most important, by means of natural selection. ”

“ In the first place, the individuals which, primarily in growth and secondarily in smaller developments of less-important organs, are by implication inferior, are likely to be eliminated from the species. In the second place, differences of structure produced in the way shown do not express differences of constitution—are not the effects of somewhat divergent physiological units ”

“ But the study of the relations of the organism to its environment, organic and inorganic, also belongs to physiology in the wider sense; we call this part of it perilogy, or the physiology of relations. To this belong chorology, or the science of distribution (also called biological geography, as it deals with geographical and topographical distribution) , and œcology or bionomy (also recently called ethology) , the science of the domestic side of organic life, of the life-needs of organisms and their relations to other organisms with which they live (biocenosis, symbiosis, parasitism) . ”

“ But when an organism undergoes a great change of structure during development, the cells, which at each stage are supposed to be directly derived from previously-existing cells, must likewise be greatly changed in nature ”

“ We turn thus from the RESULTS of the selection of favorable variations to the biological PROCESSES by which organisms become accommodated to their conditions of life.
At once the old questions arise. Are these processes fundamentally peculiar to the life of organisms? Does the capacity of the organism thus to adjust itself to its environment involve factors not found in the operations of inorganic nature? Our answers will be determined essentially by the nature of our interest in the organism—whether we regard its existence as the END or merely an incidental EFFECT of its activities. ”

“ Conversely, under the reactions of functions on structures in individual organisms, come the facts showing that functions, when fulfilled to their normal extents, maintain integrity of structure in their respective organs; and that within certain limits increases of functions are followed by such structural changes in their respective organs, as enable them to discharge better their extra functions. ”

“ No matter what we may call this point of vital activity in a cell--whether it be a bioplast, a plastid, a physiological unit, or a granule of "elementary life-stuff"--it simply performs the one single function of life to which it is specifically assigned in the process of "building up" any one identical individual of a species, whether it be a man, an ape, a tree, or a parasitic fungus. ”

“ ESSENTIAL NATURE OF THE ORGANISM.
The essential nature of a thing is the sum total of its causes and effects. Organisms arise from a germ cell which consists of idioplasm and in turn they produce like germ cells. Their nature depends also on their idioplasm, i.e., on the sum total of their idioplasmic determinants. Observation of organisms, even in their fullest life history, gives us an imperfect and even false conception of their true nature. ”

“ Biotic organization proper consists of some kind of combination of the biological units or cells into tissues and organs, thus forming a compound or complex body called an organism. Such combinations are formed in a great variety of ways and the primary units are integrated in all degrees. In the highest organisms there is complete integration and interdependence of parts. ”

“ It is clear that natural selection in the sense of individual or "personal" selection cannot adequately explain the origin of functional structure and the functional harmony of structure, for thousands of cells would have to vary together in a purposive way before any real advantage could be gained in the struggle for existence, and it is in the highest degree unlikely that this should come about by chance variation. [486] The development of purposive internal structure is only to be explained by the properties of the tissues concerned. ”

“ Let us begin our studies of adaptations in a field which may justly be called a connecting link between morphogenesis and physiology proper, not yet wholly separated from the science of the organic form, morphology. ”

“ If we clearly recognize that the physical basis of life is the same in both plant and animal, and that it is through disturbance, primarily, of the protoplasmic functions that the functions of the organism as a whole are disordered, then from this and what has already been stated it becomes evident that the pathology of plants and animals is the same, chiefly involving greater degrees of complexity in the latter, and that we must apply the same principles for the recognition of disease in each case. ”

“ All the physiological activities of animals and plants—assimilation, secretion, excretion, motion, generation—are the expression of the activities of the cells considered as physiological units. Each individual, among the higher animals and plants, is a synthesis of millions of subordinate individualities. ”

“ Dealing with biological phenomena as phenomena of evolution, we have to interpret not only the increasing morphological heterogeneity of organisms, but also their increasing physiological heterogeneity, in terms of the re-distribution of matter and motion. ”

“ In order the more thoroughly to investigate these matters it is necessary to consider the mode of growth, and specially the plan of evolution or development of each organ. This is the more needful owing to the common origin of things ultimately very different one from the other, and to the presence of organs which, in the adult state, are identical or nearly so in aspect, but which nevertheless are very unlike in the early stages of their existence. ”

“ Organic evolution takes place only on condition that the masses of protoplasm formed of the physiological units, and of the assimilable materials out of which others like themselves are to be multiplied, are subject to heat of a given degree—are subject, that is, to the unceasing impacts of undulations of a certain strength and period ”

“ Indeed, as will be seen at the proper time, the mysteries of daily occurrence, such as growth, budding, and reproduction, are as great as any which beset the passage from form to form, from species to species. No one who has thought of it sufficiently can deny that the ordinary facts of generation, as the necessity of the union of two cells of nearly-spent vitality to produce a third cell, or a brood of cells, endowed with primeval vigor, present difficulties more unsurpassable than the origin of the germs of living things from inorganic matter ”

“ In the case of very small animals, and of individual cells, the principle becomes especially important, in consequence of the molecular forces whose action is strictly limited to the superficial layer. ”

“ And of like natures are the criticisms which must be passed on the generalization, that cells are the morphological units of organisms. To continue the simile, the truth turns out to be, that the primitive clay or protoplasm out of which organisms are built, may be moulded either directly, or with various degrees of indirectness, into organic structures. The physiological units which we are obliged to assume as the components of this protoplasm, must, as we have seen, be the possessors of those proclivities which result in the structural arrangements of the organism. ”