Bacteria

“ Latterly bacteriologists have come to understand that it is not so much the presence of organisms which is injurious to man and other animals, as it is their products which cause the mischief; and the amount of toxic product bears no known proportion to the degree of invasion by the bacteria. The various and widely differing modes of action in bacteria are therefore dependent upon these three elements: the tissues or medium, the bacteria, and the products of the bacteria; and in all organismal processes these three elements act and react upon each other. ”

“ 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. ”

“ 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. ”

“ Sometimes a bacterium can be readily recognized from one or two characters, but not infrequently a whole series of tests must be made before the species is determined. As our knowledge has advanced it has become abundantly evident that the so-called pathogenic bacteria are not organisms with special features, but that each is a member of a group of organisms possessing closely allied characters. From the point of view of evolution we may suppose that certain races of a group of bacteria have gradually acquired the power of invading the tissues of the body and producing disease. ”

“ Spores, as the seeds of plants, often seem to be produced when the conditions are unfavorable; the bacterium then changes into this form, which under natural conditions is almost indestructible and awaits better days.
The bacteria are divided into species, the classification being based on their forms, on the mode of growth, the various substances which they produce and their capacity for producing disease. The differentiation of species in bacteria is based chiefly upon their properties, there being too little difference in form and size to distinguish species. ”

“ 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. ”

“ The normal living tissues have an inimical effect upon bacteria. Saprophytic bacteria of various kinds are normally present on exposed surfaces of skin or mucous membrane. Tissues also which are dead or depressed in vitality from injury or previous disease, but which are still in contact with the tissues, afford an excellent nidus for the growth of bacteria. Still these have not the power, unless specific, to thrive in the normal living tissue. ”

“ It would be difficult to say where bacterium germs do not exist. In air, in water, in the soil adhering to tiny particles of every kind, in every region of the earth, from the poles to the equator, they are found. In the substance of the tissues—nay, in the cells of almost all plants, and in the interstices of the tissues of many animals—bacteria germs exist. I know not what part of the body of man and the higher animals is entirely destitute of particles which under favorable circumstances develop into bacteria. ”

“ Another important method consists in inoculating an animal with some fluid containing the various bacteria. A pathogenic bacterium present may invade the body, and may be obtained in pure culture from the internal organs. This method applies especially to pathogenic bacteria whose growth on culture media is slow, e.g. the tubercle bacillus. ”

“ The common belief that all or even most bacteria are harmful is quite unfounded. As a matter of fact, while not less than 1500 different kinds of micro-organisms or germs are known, only about 75 varieties are known to produce disease.
Most bacteria belong to the class of micro-organisms called saprophytes, which find their food in dead organic matter, both animal and vegetable, and cannot flourish in living tissues. ”

“ Hence bacteria are indispensable in nature, especially in keeping up the circulation of nitrogen. They are also of great service in the circulation of carbon, sulphur and phosphorus. Though some few kinds cause disease in man and animals, if it were not for the saprophytic bacteria above outlined, there could be no animals and higher plants to acquire these diseases. ”

“ Just as an unidentified disease in an animal may be determined by testing its serum as above described against known kinds of bacteria, so unknown bacteria isolated from an animal, from water, etc., may be identified by testing them against the blood sera of different animals, each of which has been properly inoculated with a different kind of known bacteria. If the unknown organism is agglutinated by the blood of one of the animals in high dilution, and not by the others, evidently the bacterium is the same as that with which the animal has been inoculated, or immunized, as is usually stated. ”

“ But even yet some botanists claim that all bacteria are but one species, appearing under different forms according to their surroundings, and that these forms are mutually convertible. The question is a difficult one to answer, since bacteria of widely differing powers may resemble each other in form. Hence, if a species cultivated in a flask be contaminated by other germs accidentally introduced, which is very likely to happen, the gravest errors may arise. ”

“ In this method the bacteria are distributed in a gelatine or agar medium liquefied by heat, and the medium is then poured out on sterile glass plates or in shallow glass dishes, and allowed to solidify. Each bacterium capable of growth gives rise to a colony visible to the naked eye, and if the colonies are sufficiently apart, an inoculation can be made from any one to a tube of culture-medium and a pure culture obtained. ”

“ There is no well-defined limit between ferments and bacteria, any more than between ferments and fungi, or again, between fungi and bacteria. Their smaller size is the principal difference which separates bacteria from ferments, although there are bacteria of large size, such as are so frequently found in the mouth of even a healthy man, and which much resemble in their mode of growth some of the lower fungi.—Trouessart. ”

“ Owing to the short time which has been devoted to the study of bacteria and their functions, closer attention has been paid to the harmful or pathogenic bacteria because of their relation to human health. This one-sided study of bacteriology has blinded us to the beneficent action of many bacteria, and has caused us much unnecessary fear of their presence in food. ”

“ The Bacteria, like the Chromacea, have no nucleus. As is well-known, they play an important part in modern biology as the causes of fermentation and putrefaction, and of tuberculosis, typhus, cholera, and other infectious diseases, and as parasites, etc. But we cannot linger now to deal with these very interesting features; the Bacteria have no relation to man's genealogical tree. ”

“ 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. ”

“ Moreover, these species of bacteria are found with almost absolute constancy in and around the body, even in health. They are on the clothing, on the skin, in the mouth and alimentary canal. Here they exist, commonly doing no harm. They have, however, the power of doing injury if by chance they get into wounds. But their power of doing injury varies both with the condition of the individual and with variations in the bacteria themselves. ”

“ In other words, may not a bacterion, pure and simple, by being brought into contact with some form of degenerate tissue, acquire or give rise to other bacteria which possess certain characteristics which we recognize as being those of special disease, and that those characteristics enable them to excite a similar form of disease in the new nidus? ”

“ The kind of bacterium to be destroyed, since some are more readily killed by a given disinfectant than others, even though no spores are present.
2. The age of the culture. Young bacteria less than twenty-four hours old are usually more readily killed than older ones since the cell wall is more delicate and more easily penetrated, though old growths may be weakened by the accumulation of their products and be more easily destroyed. ”

“ To the busy investigator who cannot afford either the time or space in which to maintain a large bacterial family, it is of immense convenience to be able to obtain at a moment's notice a trustworthy culture, say, of typhoid or tuberculosis, or specimens of obscurer origin from air or water for purposes of investigation. These bacterial cultures are all guaranteed pure, free from contamination or admixture with other and alien micro-organisms, and are strictly what they are represented to be. ”

“ 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. ”

“ While some bacteria perhaps produce results by a different method, we must recognise the production of poisons as at all events the common direct cause of the symptoms of disease. This explanation will enable us more clearly to understand the relation of different bacteria to disease. ”

“ But, be that as it may, the micro-organisms themselves, by their own bodily presence, set up changes and perform functions which may have far-reaching effects. It is obvious that the wider the distribution the wider is the area of tissue change, and vice versâ. Yet there is something of far greater importance than the mere presence of bacteria in human or animal tissues; for the secondary action of disease-producing germs—and possibly it is present in all bacteria29—is due to their poisonous products, or toxins, as they have been termed. ”

“ The qualitative discrimination of the bacteria present in dust has resulted in the discovery of, amongst other disease germs, the consumption bacillus, the lock-jaw or tetanus bacillus, bacteria associated with diphtheria, typhoid fever, pulmonary affections, and various septic processes. ”

“ 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. ”

“ No single micro-organism is found to be the specific exciter of the summer diarrhœa of infants, but the affection is generally to be attributed to the result of the activity of a number of varieties of bacteria, some of which belong to well-known species, and are of ordinary occurrence and wide distribution, the most important being the streptococcus and Proteus vulgaris. ”

“ The practical use of these agents for the direct destruction of bacteria in diseases of man or animals is restricted to those cases where they may be applied directly to the diseased area, since they are just as injurious to the animal cell as they are to the bacteria, and even more so. Their skilful use as stimuli to the body cells to enable them to resist and overcome bacteria and other injurious organisms or cell growths is an entirely different function and will not be considered here. ”

“ Their minuteness, their capability of being physically demonstrated, the absolute necessity of their presence to the origination of bacteria in sterilized infusions of any and every kind, taken in connection with what we know concerning the germs of the heteromita whose life-histories have been studied, render it simply inevitable that we have at length reached, what we are justified in believing to be, a genetic product of the bacteria through which their continuation as organisms is preserved. ”