Protist

“ But though it may be more scientific, from a theoretical point of view, to group all these primitive organisms together in the way suggested by Haeckel, in practice it is inconvenient, on account of the vast number of forms of life to be comprised as Protista, their diversity in habit of life and organization, and, above all, the difference in the technical methods required for their study, which becomes too complicated for a single worker. Hence Protistology becomes split up in practice by its own mass into three sciences: the Bacteria are the objects of the science of bacteriology ”

“ What would the human mind be if we could not read, write, and draw, and have a direct knowledge through the eye of the forms and colors of the outer world? Yet this invaluable structure is only the highest and most perfect stage in the long chain of evolutionary processes which has its starting-point in the general sensitiveness to light, or the photic irritability of plasm. However, we find a number of varieties and grades of this even among the unicellular protists, and, indeed, the very lowest and oldest of the protists, the monera. ”

“ For the protists, the unicellular organisms (without tissue) exhibit a much greater freedom and variety in the development of their fundamental forms than the histons, the multicellular tissue-forming organisms. In the protists (both protophyta [172] and protozoa) the constructive force of the elementary organism, the individual cell, determines the symmetry of the typical form and the special form of its supplementation; but in the histons (both metaphyta and metazoa) it is the plasticity of the tissue, made up of a number of socially combined cells, that determines this. ”

“ Many evolutionary innovations are found only in eukaryotes, some of which are present in all lineages (e.g., the cytoskeleton, nucleus) and others that are restricted to a few lineages (e.g., multicellularity, photosynthetic organelles [plastids] ) . These and other eukaryotic features evolved within microbial eukaryotes (protists) that thrived for hundreds of millions of years before they gave rise independently to multicellular eukaryotes, the familiar plants, animals, and fungi [1] . ”

“ A number of eminent zoologists—Weismann being particularly prominent—have recently defended the opinion that only the lowest unicellular organisms, the protists, are immortal, in contradistinction to the multicellular plants and animals, whose bodies are formed of tissues. ”

“ In the first place, the extremely small size and isolation of the vegetative cells place the protoplasmic contents in peculiarly favourable circumstances for action, and we may safely conclude that, weight for weight and molecule for molecule, the protoplasm of bacteria is brought into contact with the environment at far more points and over a far larger surface than is that of higher organisms, whether—as in plants—it is distributed in thin layers round the sap-vacuoles, or—as in animals—is bathed in fluids brought by special mechanisms to irrigate it. ”

“ Others consider the bacterium as formed of protoplasm containing granules capable of being colored, which are a part of the protoplasm itself, and not a nuclear substance. On the latter view, bacteria would consist of cell plasm enclosed in a membrane and destitute of a nucleus. Whatever be the nature of the granule-containing material, each bacterium is regarded as a cell, the minutest and simplest living particle capable of an independent existence that has yet been discovered. ”

“ Each one possesses a firm cell-wall, filled with living matter; in an earlier chapter, we described the one called protean animalcule and, although it was composed of but a single cell it had no definite wall. This is one of the essential differences between plants and animals, both of them are made up of one or more, maybe millions of cells, but each plant cell is surrounded by a well-defined wall, animal cells have no such walls. The exact position of the bacteria in the plant world is still open to doubt. Most scientists place them amongst the fungi ”

“ Under no conditions is multiplication so rapid as with the bacteria, and in general the simpler the form of organism the more rapid is the multiplication. It is common to all of the protozoa to develop forms which have great powers of resistance, this being due in some cases to encystment, in which condition a resistant membrane is formed on the outside, in others to the production of spores. A fluid environment is essential to the life of the protozoa, but the resistant forms can endure long periods of dryness or other unfavorable environmental conditions. ”

“ The foregoing definition does not distinguish the Protozoa sharply from the primitive forms of plant-life, with which, as stated above, they are connected by many transitions; but the differentiation of the body-substance into nucleus and cytoplasm separates them at once from the Bacteria, in which the chromatin is distributed evenly through the body-protoplasm. ”

“ The cells of the Bacteria are constructed like other plant-cells in so far as their diminutive size has allowed us to observe them. The cell-wall only exceptionally shows the reactions of cellulose (in Sarcina, Leuconostoc; also in a Vinegar-bacterium, Bacterium xylinum) ; a mucilaginous external layer is always present. The body of the cell mostly appears to be an uniform or finely granulated protoplasm. Very few species (e.g. Bacillus virens) contain chlorophyll; others are coloured red (purple sulphur Bacteria) ; the majority are colourless. ”

“ The protozoa, like the bacteria, are unicellular organisms and contain a nucleus as do all cells. They vary in size from forms seen with difficulty under the highest power of the microscope to forms readily seen with the unaided eye. Their structure in general is more complex than is the structure of bacteria, and many show extreme differentiation of parts of the single cells, as a firm exterior surface or cuticle, an internal skeleton, organs of locomotion, mouth and digestive organs and organs of excretion. ”

“ The second key criterion that is used to polarize the evolutionary transition and place the root of the tree within negibacteria is the distribution of the proteasome core particle. It is present in archaea (20S proteasome) , in eukaryotes (26S proteasome) and in some, but not all, actinobacteria (high GC Gram positive) . The two, α and β subunits, are distantly related to HslV, a protein widely distributed in bacteria, although absent from cyanobacteria and chlorobacteria (chloroflexi) . ”

“ One of them refers to the structure of protoplasm as revealed by the microscope. Throughout the whole of the living kingdom, from the bacteria studied by Kunstler and Busquet to the most complicated protozoa, protoplasmic matter presents the same constitution, and in consequence, this structure of the protoplasm must be considered as one of its distinctive characters. It is not homogeneous; it is not the last term of the visible organization: it is itself organized. Experiment shows that it does not resist breaking up or crushing. Mutilations cause it to lose its properties. ”

“ The plants, that is, the higher plants, are not able to live on their own proteids as the animals are. But there are lower plants, certain kinds of bacteria, that can break up the big complicated proteid molecules into their component parts and reduce the nitrogen in them to ammonia or ammonia-like compounds. Having done this they stop and turn over the job to another set of bacteria to be carried through the next step. For you must know that soil society is as complex and specialized as that above ground and the tiniest bacterium would die rather than violate the union rules. ”

“ Another step further and we arrive at cell complexes having definite functions, which we call organs. But even the most developed organisms, both of the animal and plant worlds, have relations with cells which stand outside the common organization. By means of micro-organisms the plant gains access to otherwise inaccessible sources of nitrogen, while by means of bacteria the animals make use of the important carbohydrate, cellulose. The bacteria convert the latter, within the intestines, into products which can be further decomposed by the ferments secreted by the glands. ”

“ Cranmer the elder, through use of an undescribed (in the notebook) growth medium of which one constituent was agar-agar, and the use of radium emanations, had succeeded in bringing about apparently unrestricted growth in the paramœcium protozoan, certain of the vegetable growths (among which were bacteria) , and in the amorphous cell of protoplasm known as the amœba—the last a single cell containing only neucleolus, neucleus, and a space known as the contractile vacuole which somehow aided in throwing off particles impossible [30] to assimilate directly. ”

“ In white light, the bacteria will be seen to precipitate themselves upon the grains of chlorophyl, to get the oxygen disengaged from them. They thus constitute a very delicate reagent. To witness the effect of the different colors, we let the microscopic spectrum fall upon a filament of conferva, or a transverse leaf-section. The bacteria will collect upon the plant in the red, at the point of maximum absorption, next in the blue, and the density of the population will nearly follow the absorption-curve of the coloring-matter. ”

“ Very careful chemical investigations on pure cultures will be necessary before the chaos of phenomena presented by putrefactive bacteria can be arranged in something like order.
In the decomposition of proteids five or rather six stages may be distinguished. "Proteids are split up by putrefaction into a large number of simpler compounds both nitrogenous and non-nitrogenous. The substances thus produced are precisely similar to those resulting from the artificial decomposition of proteids by fusion with caustic potash or boiling with hydrochloric acid or barium hydrate. ”

“ On the outside is a cell membrane which encloses cytoplasm and nucleus; the latter, however, is not in a single mass, but the nuclear material is distributed through the cell. Many of the bacteria have the power of motion, this being effected by small hair-like appendages or flagellæ which may be numerous, projecting from all parts of the organisms or from one or both ends, the movement being produced by rapid lashing of these hairs. A bacterium grows until it attains the size of the species, when it divides by simple cleavage at right angles to the long axis forming two individuals. ”

“ In many cases the digestion of reserve food materials is effected by the direct action of the protoplasm, without the intervention of enzymes. This property of living substance can be proved in the case of the cells of the higher plants, but it is especially prominent in many of the more lowly organisms, such as the Bacteria. The processes of putrefaction may be alluded to as affording an instance of such a power in the vegetable organisms. At the same time it must be remembered that the secretion of enzymes by Bacteria is of widespread occurrence. ”

“ As, moreover, the first thing which a cell does when it grows is to divide, the whole proceeding looks rather futile. But ready-made protoplasm of an assimilable shape is rare, and it is not often that a cell, unless it be a plant or a parasite, finds itself in a substance which can be handed straight to the nucleus without further elaboration. Usually the cell has to discharge from itself a reagent, which will develop the right chemical qualities in the matter it wants to absorb. This substance is known as an enzyme, or ferment. ”

“ Chemistry of individual proteins is important to life, but the organism must be put back into bacteriology and evolutionary biology, which have recently been dominated by fragmentary gene-, sequence-, and molecule-oriented oversimplifications [ [1] . Cyanobacteria is an excellent example of a bacterial phylum enduringly defined on organismal grounds a century before sequencing was invented and which retained its organismal integrity, essential physiological properties, and typical cell structure for at least 2.4, and probable over 2.7 billion years despite lateral gene transfer ”

“ Since the number of different reactions which take place within a living cell is very great, and since these chemical changes are extremely variable in type, it follows that the number of different enzymes which must exist in either a plant or an animal organism is likewise very large. For example, fourteen different enzymes have been isolated from the digestive system, and at least sixteen from the liver, of animals. They are universally present in living protoplasm of every kind, from the most minute bacterium to the largest forest trees, in the plant kingdom ”

“ But yeast-fungi and mould-fungi, like bacteria or fission-fungi, are micro-organisms, belonging to two specific orders, the Saccharomycetes and the Hyphomycetes, which are intimately related to each other, but quite distinct from bacteria. Their germs occur widely distributed in air, soil, and water. Many species are of hygienic, while others are of pathological interest and importance in being either accidentally associated with, or the cause of, disease processes, while others are fermentations of very essential service in various industrial processes. ”

“ I have discovered that for an efficient bate a pure culture or single species of bacteria is insufficient, and that no single organism hitherto isolated will give results equal to dung. I have also discovered that the production of enzymes of the character above referred to, depends more upon the composition of the nutrient medium in which the bacteria are cultivated, than upon the kind of bacteria, although these latter must be capable of producing the required enzymes, the production of which appears to be due to a symbiotic growth of bacteria at present little understood. ”