Microorganism

“ In order that any organism may thrive there are a number of general environmental conditions which must be fulfilled. These conditions vary more or less for each kind of organism. Bacteria are no exception to this general rule. These conditions may be conveniently considered under the general heads of moisture; temperature; light; oxygen supply; osmotic pressure; action of electricity; of Röntgen and radium rays; pressure; mechanical vibration; and chemical environment, including the reaction of the medium, the effect of injurious chemicals, and especially the food requirements of bacteria. ”

“ We have already seen how many organisms exhibit their energy in the formation of many coloured pigments. They are, as a rule, "innocent" microbes. Oxygen is required for some, darkness for others, and they all vary according to the medium upon which they are growing. Red milk, yellow milk, and green pus afford examples of pigment produced by bacteria.
2. Gas. Quite a number of the common bacteria, like Bacillus coli, produce gas in their growth; hydrogen (H) , carbonic acid (CO2) , methane (CH4) , and even nitrogen (N) being formed by different bacteria. ”

“ It will be noticed that the next step in the food cycle is taken by the decomposition bacteria. These organisms, existing, as we have already seen, in the air, in the soil, in the water, and always ready to seize hold of any organic substance that may furnish them with food, feed upon the products of animal life, whether they are such products as muscle tissue, or fat, or sugar, or whether they are the excreted products of animal life, such as urea, and produce therein the chemical decomposition changes already noticed. ”

“ Not only in the diagnosis and treatment of disease, nor even in the various applications of preventive medicine, but in ever-increasing degree and sphere, micro-organisms are recognised as agents of utility or otherwise no longer to be ignored. They occur in our drinking water, in our milk supply, in the air we breathe. They ripen cream, and flavour butter. They purify sewage, and remove waste organic products from the land. They are the active agents in a dozen industrial fermentations. They assist in the fixation of free nitrogen, and they build up assimilable compounds. ”

“ It will be recalled that bacteria are a vegetable form of life; that, like all plants, they have, under certain conditions, the power of growth which is shown, largely, by their reproduction; and that under other conditions they are killed. When their growth is merely checked, they are in a dormant state, or perhaps form spores, in either of which cases they are ready to develop as soon as their environment permits. Temperature has much to do with the state of bacteria. ”

“ Movements.—Movements, if slight and simply of a flowing character, do not appear to injuriously affect the growth of bacteria; but violent agitation, such as shaking, absolutely kills them.
A condition of perfect rest would seem to be that most conducive to bacterial growth.
The Metabolic Products of Bacteria.—Pigment Production.—Many micro-organisms produce one or more vivid pigments—yellow, orange, red, violet, fluorescent, etc.—during the course of their life and growth. The colouring matter usually exists as an intercellular excrementitious substance. ”

“ We shall also show that all living organisms, such as seeds, fungus-spores, morphological cells, etc., perish at a temperature of about 100° C., and that Bacteria, Torulæ, and other infusorial forms, making their appearance in super-heated flasks, originate not from morphological cells, plastide particles, bioplasts, or any other vital organism, but from indestructible vital units, which are everywhere present in the organic matter of our globe, and ready to burgeon forth into life whenever the necessary vital conditions exist, and the proper incidences of environment occur. ”

“ 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. ”

“ By working through some such scheme as the above we are able to detect what quantity and species of organisms, saprophytic or parasitic, a water or similar fluid contains. For, observe what information we have gained. We have learned the form (whether bacillus, micrococcus, or spirillum) , size, consistence, motility, method of grouping, and staining reactions of each micro-organism; the characters of its culture, colour, composition, presence or absence of liquefication or gas formation, its rate of growth, smell, or reaction ”

“ During their growth the bacteria live upon the fluid, as all other plants do upon their soil. Characteristic, however, of bacteria-growth is the decomposition of any complex organic substances in the fluid to an extent entirely disproportionate to the weight of the bacteria themselves. This destructive action occurs wherever bacteria exist, be it in the experimental fluid, or in the solid animal or vegetable refuse where they are ordinarily found. It constitutes, in fact, rotting or putrefaction. ”

“ Innumerable small organisms (known as microbes, bacteria, bacilli, or germs) exist in the air, and in or upon nearly all substances. These organisms or germs are so small that they are invisible to the eye unless a powerful microscope is used. They are so small that thousands of them can assemble on the head of a pin or in the smallest drop of water. |Harmless bacteria.| Most of them are harmless; and some of them render useful service. Without the aid of these little organisms we could not make cheese or vinegar. ”

“ Neither the cane-sugar nor the common salt themselves injure the bacteria chemically, but by the high concentration prevent their development. In drying material in order to preserve it there are two factors involved: first, the loss of water necessary for growth and second, the increased osmotic pressure.
In a medium of greater density diffusion of water is outward from the cell and this will continue until an equilibrium is established between cell contents and medium. Food for the organism must be in solution and enter the cell by diffusion. ”

“ We cannot enter into a full discussion of the rôle of bacteria in industrial processes, but several of the chief directions may be pointed out. Without exception, bacteria have a part in them on account of their powers of fermentation. In securing their food, bacteria break down material, and bring about chemical and physical change. The power which organisms have of chemically destroying compounds is in itself of little importance, but the products which arise as a result are of an importance in the world which has not hitherto been recognised. ”

“ Finally, we must refer to the numerous bacteria that occasion putrefaction in vegetable or animal organisms. These microbes, which float in the air, fall upon dead animals or plants, develop thereon, and convert into mineral matters the immediate principles of which the tissues are composed, and thus continually restore to the air and soil the elements necessary for the formation of new organic substances. ”

“ Roux and some other eminent bacteriologists suggest that bacteria should be classified according to their method of spore formation.
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THE INFLUENCE OF EXTERNAL CONDITIONS ON GROWTH OF BACTERIA
Nutritive Medium. In the very earliest days of the study of micro-organisms it was observed that they mostly congregate where there is pabulum for their nourishment. The reason why fluids such as milk, and dead animal matter such as a carcass, and living tissues such as a man's body contain so many microbes is because each of these three media is favourable to their growth. ”

“ CHAPTER IV. BACTERIA IN NATURAL PROCESSES.—AGRICULTURE. Thus far, in considering the relations of bacteria to mankind, we have taken into account only the arts and manufactures, and have found bacteria playing no unimportant part in many of the industries of our modern civilized life. So important are they that there is no one who is not directly affected by them. There is hardly a moment in our life when we are not using some of the direct or indirect products of bacterial action. ”

“ Presence of spores, since they are much more resistant than the growing cells.
4. Whether the organism is a “good” or “bad” growth, i.e., whether it has grown in a favorable environment and hence is vigorous, or under unfavorable conditions and hence is weak.
5. The number of bacteria present, since with chemical agents the action is one of relative masses.
6. Nature of the substance in which the bacteria are. Metallic salts, especially bichloride of mercury, are precipitated by albuminous substances and if employed at all must be used in several times the ordinary strength. ”

“ 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. ”

“ Conditions of Bacterial Life.#--Bacteria require for their growth and development a suitable food-supply in the form of proteins, carbohydrates, and salts of calcium and potassium which they break up into simpler elements. An alkaline medium favours bacterial growth; and moisture is a necessary condition; spores, however, can survive the want of water for much longer periods than fully developed bacteria. The necessity for oxygen varies in different species. ”

“ So far, then, the study of parasitic organisms had at an early period shared largely in my microscopical work, extending over several years, and with the result that these micro-organisms were found to exhibit on occasions great diversity of character, and that different members of the bacteria in particular flourish under great diversity of action, and often under entirely opposite conditions; that they feed upon wholly different materials, and perform an immense variety of chemical work in the media in which they live. ”

“ Many pathological observations have proved, that certain micro-organisms require a so-called mixed infection, that is, that certain bacteria alter the cell substance of the host in such a way, that some other kind of bacterium finds conditions favourable for its existence. ”

“ With many bacteria, especially those that affect proteid matter, foul-smelling gases are formed. These are known as putrefactive changes. All organic matter, under the action of various organisms, sooner or later undergoes decay, and in different stages of these processes, acids, alkalies, gases and numerous other products are formed. Many of these changes in organic matter occur only when such material is brought in direct contact with the living bacterial cell. ”

“ Or media in which certain organisms thrive and others not, so that the former soon “crowd out” the latter (unsterilized milk for lactic acid bacteria, inorganic media in soil bacteriology) may be used. A combination of the general methods (b) and (c) is much used in the separation of the organisms of the “intestinal group” in human practice. (d) The inoculation of a susceptible animal with a mixture suspected to contain a given pathogenic bacterium frequently results in the development of the latter in pure culture in the body of an animal, from which it may be readily recovered. ”

“ A microscopic vegetable organism, belonging to the class Alg‘, usually in the form of a jointed rodlike filament, and found in putrefying organic infusions. Bacteria are destitute of chlorophyll, and are the smallest of microscopic organisms. They are very widely diffused in nature, and multiply with marvelous rapidity, both by fission and by spores. Certain species are active agents in fermentation, while others appear to be the cause of certain infectious diseases. ”

“ Micro-organisms grow on food, causing it to spoil. The common growths are simple yeasts, molds, and bacteria. Because these micro-organisms are everywhere—in the air, water, soil and on all surfaces they contact—they naturally occur on all foods. Storing and preserving foods properly controls or inhibits the growth of micro-organisms, thus maintaining both quality and safety of the food. ”

“ In unpolluted water, containing only water bacteria and a very small amount of organic matter, very little or no multiplication takes place, and the growth of the water bacteria liquefying gelatine is checked to a remarkable extent. ”

“ Certain media possess the power of inhibiting the growth of a greater or less number of species. For instance, media containing carbolic acid to the amount of 1 per cent. will inhibit the growth of practically everything but the Bacillus coli communis.
5. Differential Incubation.—
In isolating certain bacteria, advantage is taken of the fact that different species vary in their optimum temperature. ”