Bacteriology

“ At first sight, the bacteria appear too minute to figure largely in human affairs, but a great department of natural science—bacteriology—has been opened by the study of their activities, and it must be admitted that the development of the science of bacteriology has been of great practical importance. The knowledge derived from experimental studies of the bacteria has been the chief source of light in an obscure domain which profoundly affects the well-being of mankind. ”

“ Having glanced hastily at the history of bacteriology, we may next consider some facts concerning the germs themselves. What are they? To the lay mind the words germ, microbe, bacterium, and bacillus often convey confused ideas of invisible, wriggling, worm-like creatures, enemies of mankind, ever on the watch to gain a stealthy entrance into our bodies, where they wreak harm and death. Scientifically considered, however, they are the smallest of living things yet known. They are not animals, but are members of the vegetable kingdom, and are possessed of definite yet varying shapes. ”

“ I must, however, first direct attention to a well-recognised fact, that bacteriology only touches animal pathology at a few points, and that so far from bacteria being synonymous with disease germs, the majority of these remarkable organisms appear to be beneficent rather than inimical to man. ”

“ In this way, and even before any minute and systematic study of bacteria,—i.e., before the inauguration of bacteriology as a separate department of scientific study,—it was practically established that the agencies which produce putrefactive changes or fermentation were minute particles which were ever present in almost every substance, and that by heat or something corresponding to filtration it was possible to remove them or destroy their activity. ”

“ By the middle of the century, however, observations on bacteria, largely as the result of the labors of botanists, were accumulating, and views about spontaneous generation, fermentation and infection were being discussed, but the fundamental experiments necessary to settle these problems were yet to be made, and, curiously enough, it was to a chemist, influenced by the methods of physics, who was to establish bacteriology as a biological science and to give to it the important place in medicine which it has occupied for the past thirty years. ”

“ The recommendation of sanitarians that water or milk or food suspected of being contaminated by pathogenic bacteria should be exposed to a boiling temperature before it is used is based upon the experimental data referred to; and the knowledge that organic liquids can be sterilized by heat constitutes the foundation upon which the bacteriology of the present day has been established. To obtain reliable information with reference to the biological characters of any particular micro-organism it is necessary to experiment with pure cultures, and this requires a sterile culture medium. ”

“ 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. ”

“ 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. ”

“ CHAPTER IV. THE BACTERIOLOGY OF THE BATE.
“Omne vivum ex ovo.”—Harvey (1578–1675) .
When a drop of liquid from a puer wheel in use is examined under the microscope73 with 1/12 o.i. objective, it is seen to be swarming with bacteria.
The majority are short rods (bacilli) , but other forms, cocci and spirilli, are seen in lesser numbers. Most of these bacteria move briskly in the liquid; as the temperature of the slide sinks, their movements become slower, and finally cease. The illustration, Fig. 14, shows the various forms of bacteria observed by the author in puer liquors × 1000 diam. ”

“ Experimental medicine has added constantly to the list of diseases caused by bacterial organisms, and the general public has been educated to an adequate conception of the importance of the germ as the chief agency in the transmission of disease, with corresponding advantage to the efficiency of personal and public hygiene. At the same time knowledge of the benign bacteria and the enormous role they play in the industries and the arts has become much more widely diffused. Bacteriology is being studied in colleges as one of the cultural sciences ”

“ Another method which is frequently applicable with material from human or animal sources is to (3) rub the material over the surface of a slope tube or of medium solidified in a Petri dish with a sterile heavy platinum needle, glass rod, or cotton swab. If the bacteria are not too numerous, pure cultures may frequently be obtained. ”

“ 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. ”

“ The way that the organism grows in different kinds of cultures, the by-products produced in different media, and effect on the animal body when injected into the same are also used as data in distinguishing one species from another.
Conditions favoring bacterial growth. The bacteria, in common with all other living organisms are affected by external conditions, either favorably or unfavorably. Certain conditions must prevail before development can occur. ”

“ 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. ”

“ Other bacteria derive their nitrogen from some of the products of the first two groups, and still further break down the complex protein molecule. Under normal conditions these various kinds of bacteria all occur together and thus mutually assist one another in what is equivalent to a symbiosis or rather a metabiosis, a “successive existence,” one set living on the products of the other. ”

“ Distribution of bacteria. As bacteria possess greater powers of resistance than most other forms of life, they are to be found more widely distributed than any other type. At the surface of the earth, where conditions permit of their growth, they are found everywhere, except in the healthy tissues of animals and plants. ”

“ The bacteria are so extremely small that it is impossible to study individual germs separately without the aid of first-class microscopes. For this reason, but little advance was made in the knowledge of these lower forms of plant life, until the introduction of culture methods, whereby a single organism could be cultivated and the progeny of this cell increased to such an extent in a short course of time, that they would be visible to the unaided eye. ”

“ 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. ”

“ In many respects the bacteria are most nearly related to the lowest algæ, since both are unicellular organisms, both reproduce by transverse division and the forms of the cell are strikingly similar. The bacteria differ in one important respect, that is, they do not contain chlorophyl, the green coloring matter which enables all plants possessing it to absorb and break up carbon dioxide in the light, and hence belong among the fungi. Bacteria average much smaller than even the smallest algæ. ”

“ 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. ”

“ De Lapouge recently said, "Anthropology is destined to revolutionise the political and the social sciences as radically as bacteriology has revolutionised the science of medicine." ”

“ 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. ”

“ 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. ”

“ We may summarise the vast mass of historical, physiological, and pathological research extending from 1650 to 1898 in three great periods: the period of detection of living, moving cells (Leeuwenhoek and others in the seventeenth century) ; the period of the discovery of their close relationship to fermentation and putrefaction (Spallanzani, Schulze, Schwann, in the eighteenth century) ; and, thirdly, the period of appreciation of the rôle of bacteria in the economy of nature and in the production of disease (Tyndall, Pasteur, Lister, Koch, in the nineteenth) . ”

“ 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. ”

“ The facts themselves by their remarkable variety have not aided classification. Names which a few years ago were applied to individual species, like Bacillus subtilis, or Bacterium termo, or Bacillus coli, are now representative, not of individuals, but of families and groups of species. Again, isolated characteristics of certain microbes, such as motility, power of liquefying gelatine, size, colour, and so forth, which at first sight might appear as likely to form a basis for classification, are found to vary not only between similar germs, but in the same germ. ”

“ 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. ”

“ 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. ”

“ 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. ”