Applies only to the bacterium or toxin used in its production.
Bacterium vermiforme, B.
In ordinary arable soil there exist motile rod-like bacteria, Bacterium radicicola.
One bacterium might thus produce in twenty-four hours a number of segments amounting to many millions of millions.
It should be mentioned that different genera require different races of the bacterium for the production of nodules.
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.
The formation of the blue mud is largely aided by the putrefaction of organic matter, and as a result the water deeper than 120 fathoms is extraordinarily deficient in dissolved oxygen and abounds in sulphuretted hydrogen, the formation of which is brought about by a special bacterium, the only form of life found at depths greater than 120 fathoms in the Black Sea.
The occurrence of a starch-like substance which stains deep blue with iodine has been clearly shown in some forms even where the bacterium is growing on a medium containing no starch, as shown by Ward and others.
The growth of an ordinary bacterium consists in uniform elongation of the rodlet until its length is doubled, followed by division by a median septum, then by the simul- Measure- taneous doubling in length of each daughter cell, again ment of followed by the median division, and soon (figs.
In health the blood and internal tissues are bacterium-free; after death they offer a most suitable pabulum for various bacteria; but between these two extremes lie states of varying liability to infection.
Fixation of Nitrogen.Another, and perhaps an even more important, instance of symbiotic association has come to the front during the same period, it is an alliance between the plants of the Natural Order Leguminosae and certain bacterium-like forms which find a home within the tissues of their roots.
All these terms, including the usual one of bacteria, are unsatisfactory; for " bacterium," " bacillus " and " micrococcus " have narrow technical meanings, and the other terms are too vague to be scientific. The most satisfactory designation is that proposed by Nageli in 1857, namely " schizomycetes," and it is by this term that they are usually known among botanists; the less exact term, however, is also used and is retained in this article since the science is commonly known as " bacteriology."
The supposed constancy of forms in Cohn's species and genera received a shock when Lankester in 1873 pointed out that his Bacterium rubescens (since named Beggiatoa roseo-persicina, Zopf) passes through conditions which would have been described by most observers influenced by the current doctrine as so many separate " species " or even " genera," - that in fact forms known as Bacterium, Hicrococcus, Bacillus, Leptothrix, &c., occur as phases in one life-history.
In 1870 Pasteur had proved that a disease of silkworms was due to an organism of the nature of a bacterium; and in 1871 Oertel showed that a Micrococcus already known to exist in diphtheria is intimately concerned in producing that disease.
Egg-shaped mass of zoogloea of Beggiatoa roseo-persicina (Bacterium rubescens of Lankester); the gelatinous swollen walls of the large crowded cocci are fused into a common gelatinous envelope.
Zoogloea of Bacterium merismopedioides, Zopf, containing cocci arranged in tablets.
Only three or four times as long as broad (Bacterium), or longer (Bacillus); the biscuitshaped ones are Bacteria in the early stages of division.
Formerly regarded as a distinct genus - the natural fate of all the various ' Brefeld has observed that a bacterium may divide once every half-hour, and its progeny repeat the process in the same time.
These oxidations are brought about by the vital activity of several bacteria, of which four-- Bacterium aceti, B.
Nencki showed, however, that if both these organisms occur together, the resulting products contain large quantities of normal butyl alcohol, a substance neither bacterium can produce alone.
The microscope magnifies the distance traversed as well as the organism, and although a bacterium which covers 9 - ro cm.
A new field of inquiry was, however, opened up when, by filtration a bacterium-free toxic fluid was obtained which produced the important symptoms of the disease-in the case of diphtheria by P. P. E.
(i) the discovery of a bacterium in the affected tissues by means of the microscope; (2) the obtaining of the bacterium in pure culture; and (3) the production of the disease by inoculation with a pure culture.
A pathogenic bacterium present may invade the body, and may be obtained in pure culture from the internal organs.
The full description of a particular bacterium implies an account not only of its microscopical characters, but also of its growth characters in various culture media, its biological properties, and the effects produced in animals by inoculation.
For example, various sugars - lactose, glucose, saccharose, &c. - are added to test the fermentative action of the bacterium on these substances; litmus is added to show changes in reaction, specially standardized media being used for estimating such changes; peptone solution is commonly employed for testing whether or not the bacterium forms indol; sterilized milk is used as a culture medium to determine whether or not it is curdled by the growth.
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.
It may be stated that the introduction of a particular bacterium into the tissues of the body leads to certain properties appearing in the serum, which are chiefly exerted towards this particular bacterium.
One great drawback in certain cases is that such animals are not susceptible to a given bacterium, or that the disease is different in character from that in the human subject.
It may also be mentioned that many toxins have now been obtained by growing the particular organism in a proteid-free medium, a fact which shows that if the toxin is a proteid it may be formed synthetically by the bacterium as well as by modification of proteid already present.
But this has not been proved, and hitherto no enzyme has been separated from a pathogenic bacterium capable of forming, by digestive or other action, the toxic bodies from proteids outside the body.
The result of the entrance of a virulent bacterium into the tissues of an animal is not a disease with hard and fast characters, but varies greatly with circumstances.
With regard to the subject of infection the chief factor is susceptibility; with regard to the bacterium virulence is allimportant.
Sometimes also the virulence of a bacterium for a particular kind of animal becomes lessened on passing it through the body of one of another species.
A second method is by injection of the bacterium in the dead condition, whereby immunity against the living organism may be produced.
In order that the immunity may reach a high degree, either the bacterium in a very virulent state or a large dose of toxin must ultimately be used in the injections.
So far as bacterial immunity is concerned, the anti-serum exerts its action either on the toxin or on the bacterium itself; that is, its action is either antitoxic or anti-bacterial.
" the production of a change in the corresponding bacterium whereby it becomes granular, swells up and ultimately may undergo dissolution.
Pfeiffer was the first to show that this occurred when the bacterium was injected into the peritoneal cavity of the animal immunized against it, and also when a little of the serum of such an animal was injected with the bacterium into the peritoneum of a fresh, i.e.
By this is meant the aggregation into clumps of the bacteria uniformly distributed (natiai n an indifferent fluid; if the bacterium is motile its movement is arrested during the process.
The serum of an animal immunized against the bacterium) was added to a fluid culture of this bacillus, growth formed a sediment instead of a uniform turbidity.
Gruber and Durham showed that sedimentation occurred when a small quantity of the homologous serum was added to an emul:_on of the bacterium in a small test-tube, and found that this obtained in all cases where Pfeiffer's lysogenic action could be demonstrated.
The bacterium, being a complex organic substance, may thus give rise to more than one antagonistic or combining substance.
Such an effect may be demonstrated outside the body by making a (actiopsonic suitable mixture of (a) a suspension of the particular bacterium, (b) the serum to be tested, and (c) leucocytes of a normal animal or person.
A particular bacterium had a special action in bringing about phagocytosis of that organism, and it had been found that this property was retained when the serum was heated at 55° C. It is now generally admitted that at least two distinct classes of substances are concerned in opsonic action, that thermostable immune opsonins are developed as a result of active immunization and these possess the specific properties of anti-substances in general, that is, act only on the corresponding bacterium.
Then as regards natural powers of destroying bacteria, phagocytosis aided by chemiotaxis plays a part, and it can be understood that an animal whose phagocytes are attracted by a particular bacterium will have an advantage over one in which this action is absent.
The Bacterium acidi lacti described by Pasteur decomposes milk sugar into lactic acid.
The swellings have been found to be due to a curious hypertrophy of the tissue of the part, the cells being filled with an immense number of minute bacterium-like organisms of V, X or Y shape.
If the particle enveloped by the protoplasm be of an organic nature, such as a bacterium, it undergoes digestion, and ultimately becomes destroyed, and accordingly the term " phagocyte " is now in common use to indicate cells having the above properties.
The ketone is also obtained when Bertrand's sorbose bacterium acts on glycerol; this medium also acts on other alcohols to yield ketoses; for example: erythrite gives erythrulose, arabite arabinulose, mannitol fructose, &c.
L-Arabinulose obtained from arabite and Bertrand's sorbium bacterium is a ketose.
These are found to contain large numbers of a bacterium termed Bacillus radicicola or Pseudomonas radicicola.
It appears from the observations of Maze that the bacterium can even absorb free nitrogen when grown in cultures FIG.
In the case of any bacterium discovered, observation must be made in a long series of instances in order to determine its invariable presence.
The simplest case is that in which only one variety of bacterium is present, and a " pure culture " may then be obtained at once.
Though the causal relationship of a bacterium to a disease may be completely established by the methods given, another very important part of bacteriology is concerned with the poisons or toxins formed by bacteria.
By immunity is meant non-susceptibility to a given disease, or to experimental inoculation with a given bacterium or toxin.
A third method is by injections of the separated toxins of a bacterium, the resulting immunity being not only against the toxin, but, so far as present knowledge shows, also against the living organism.
The bacterium, Clostridium pasteurianum, common in most soils, is able to utilize free nitrogen under anaerobic conditions, and an organism known as Azotobacter chroococcum and some others closely allied to it, have similar powers which they can exercise under aerobic conditions.