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.
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.
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.
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.
Tachinoides, does render it probable that the pathogenic forms also have true invertebrate hosts.
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.
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.
Various other microbes are also present in large numbers, but are not believed to be pathogenic or disease-producing in character.
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.
A pathogenic bacterium present may invade the body, and may be obtained in pure culture from the internal organs.