Of all external agents acting for evil, however, probably vegetable and animal micro-organisms with a pathogenic bent are most to be feared.
The vast majority of these organisms are not pathogenic, most are harmless and 4.,52 5.20 5.20 FIG.
If, on the other hand, any pathogenic organisms be present the results are disastrous because the tissue, deprived of its nervous trophic supply, has greatly lessened resistance.
Should these remain unbroken they constitute a natural barrier to the penetration of most pathogenic and other forms of germ-life into the parts beneath.
By the continuous injections under the skin, in increasing doses, of the toxins of certain pathogenic micro-organisms, such as that of diphtheria, an animal-usually the horse-may be rendered completely refractory to the disease.
Very many of the common domestic mammals can be successfully infected (either thus accidentally or else on purpose) with different " pathogenic " Trypanosomes, to which they succumb more or less readily, but they cannot be regarded as the natural hosts of those Trypanosomes.
Similarly with regard to the many other pathogenic Trypanosomes now known, there is undoubtedly, in each case, some indigenous wild animal tolerant of that particular form, which serves as a " latent source of supply " to strange mammals.
These facts, and the further knowledge that many bacteria never observed as parasites, or as pathogenic forms, produce toxins or poisons as the result of their decompositions and fermentations of organic substances, have led to important results in the applications of bacteriology to medicine.
Pathogenic Bacteria: Baumgarten, Pathologische Mykologie (1890); Kolle and Wassermann, Handbuch der pathogenen Mikroorganismen (1902-1904); and numerous special works in medical literature.
B.) Pathological Importance The action of bacteria as pathogenic agents is in great part merely an instance of their general action as producers of chemical change, yet bacteriology as a whole has become so extensive, and has so important a bearing on subjects widely different from one another, that division of it has become essential.
A pathogenic bacterium present may invade the body, and may be obtained in pure culture from the internal organs.
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.
Various other microbes are also present in large numbers, but are not believed to be pathogenic or disease-producing in character.
By means of " vaccination " we are enabled to induce an active immunity against infection by certain pathogenic bacteria.
Massart and Bordet, Leber, Metchnikoff and others have studied the phenomenon in leucocytes, with the result that while there is evidence of their being positively chemiotactic to the toxins of many pathogenic microbes, it is also apparent that they are negatively influenced by such substances as lactic acid.
By 1876 the anthrax bacillus had been obtained in pure culture by Koch, and some other pathogenic bacteria had been observed in the tissues, but it was in the decade 1880-1890 that the most important discoveries were made in this field.
The general principle in their preparation is to supply cutt;va- the nutriment for bacterial growth in a form as nearly g y similar as possible to that of the natural habitat of the organisms - in the case of pathogenic bacteria, the natural fluids of the body.
In the acquisition of pathogenic properties some of their original characters have become changed, but in many instances this has taken place only to a slight degree, and, furthermore, some of these changes are not of a permanent character.
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.
And Lond., 1908); Park, Pathogenic Micro-organisms (London, 5906); Sternberg, Manual of Bacteriology (with full bibliography, 2nd ed., New York, 1896); Woodhead, Bacteria and their products (with bibliography, London, 1891).
Even yet medical science has not determined the effect upon the human system of water highly charged with bacteria which are not known to be individually pathogenic. In the case of the bacilli of typhoid and cholera, we know the direct effect; but apart altogether from the presence of such specific poisons, polluted water is undoubtedly injurious.
Moreover, if a natural water is so liable to pathogenic pollution as to demand filtration of this kind, it ought at once to be discarded for an initially pure supply; not necessarily pure in an apparent or even in a chemical sense, for water may be visibly coloured, or may contain considerable proportions both of organic and inorganic impurity, and yet be tasteless and free from pathogenic pollution.
This, when attained, is undoubtedly a most important reduction in the chance of pathogenic bacteria passing into the filtered water; but much mere must be done than has hitherto in most places been done to ensure the constancy of such a condition before it can be assumed to represent the degree of safety attained.
Both the Argasidae and Ixodidae contain pathogenic species, of which the best known are the following: Ornithodoros monbata, belonging to the Argasidae, and called bibo in Uganda, monbata in Angola, and tampan on the Zambezi, is widely distributed in tropical Africa from Uganda in the north to the Transvaal in the south.
Monbata, which are known to be seriously harmful to mankind; whereas amongst the Ixodidae no human pathogenic species has been ascertained to exist, although several forms have been proved to be highly destructive to domestic mammals of different species.
But whatever merits they had as clarifiers of turbid water, the advent of bacteriology, and the recognition of the fact that the bacteria of certain diseases may be water-borne, introduced a new criterion of effectiveness, and it was perceived that the removal of solid particles, or even of organic impurities (which were realized to be important not so much because they are dangerous to health per se as because their presence affords grounds for suspecting that the water in which they occur has been exposed to circumstances permitting contamination with infective disease), was not sufficient; the filter must also prevent the passage of pathogenic organisms, and so render the water sterile bacteriologically.
Only a single pathogenic species can withstand the short boiling to which milk is ordinarily treated in domestic management, and this is the anthrax bacillus containing spores.
It is imperative that cream destined for butter-making should be free from pathogenic organisms.
Non-pathogenic) forms; these researches supply, indeed, practically all the material facts on which to base an account of the Haemoflagellates at the present day.
We cannot write quite so confidently with regard to the relation of the various pathogenic Trypanosomes to Tsetseflies (Glossinae).
Tachinoides, does render it probable that the pathogenic forms also have true invertebrate hosts.
The practical effect of the bactericidal action of solar light is the destruction of enormous quantities of germs in rivers, the atmosphere and other exposed situations, and experiments have shown that it is especially the pathogenic bacteria - anthrax, typhoid, &c. - which thus succumb to lightaction; the discovery that the electric arc is very rich in bactericidal rays led to the hope that it could be used for disinfecting purposes in hospitals, but mechanical difficulties intervene.
This method applies especially to pathogenic bacteria whose growth on culture media is slow, e.g.
The cultural as well as the microscopical characters of a pathogenic organism may be closely similar to other non-pathogenic members of the same group, and it thus comes to be a matter of extreme difficulty in certain cases to state what criterion should be used in differentiating varieties.
Abbott, Principles of Bacteriology (7th ed., London, 1905); Crookshank, Bacteriology and Infective Diseases (with bibliography, 4th ed., London, 1896); Duclaux, Traite de microbiologie (Paris, 1899-1900); Eyre, Bacteriological Technique (Philadelphia and London, 1902); Flugge, Die Mikroorganismen (3rd ed., Leipzig, 1896); Fischer, Vorlesungen fiber Bakterien (2nd ed., Jena, 1902); Gunther, Einfiihrung in das Studium der Bakteriologie (6th ed., Leipzig, 1906); Hewlett, Manual of Bacteriology (2nd ed., London, 1902); Hueppe, Principles of Bacteriology (translation, London, 1899); Klein, Micro-organisms and Disease (3rd ed., London, 1896); Kolle and Wassermann, Handbuch der pathogenen Mikroorganismen (Jena, 1904) (supplements are still being published; this is the most important work on the subject); Lofler, Vorlesungen fiber die geschichtliche Entwickelung der Lehre von der Bacterien (Leipzig, 1887); M`Farland, Text-book upon the Pathogenic Bacteria (5th ed., London, 1906); Muir and Ritchie, Manual of Bacteriology (with bibliography, 4th ed., Edin.
Understanding the recipes that make our pathogenic enemies is a huge advantage.