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are both to be regarded as the products of a reactive facts with regard to artificial immunity. The subject has process, and it is probable that the development of all occupied a large proportion of bacteriological antagonistic substances which confer the special character on literature within recent years, and our endeavour *aturaI antimicrobic sera, as well as antitoxins, will be expressed has been mainly to indicate the general laws mmun y' as the formation of bodies with specific combining affinity which are in process of evolution. When the facts of for the organic substance introduced into the system — natural immunity are examined, we find that no single toxin, bacterium, red corpuscle, etc., as the case may be. explanation is possible. Natural immunity against toxins The bacterium, being a complex organic substance, may must be taken into account, and, if Ehrlich’s view thus give rise to more than one antagonistic or combining with regard to toxic action be correct, this may depend substance. upon either the absence of chemical affinity of the living Passive immunity has thus been shown to depend upon molecules of the tissues for the toxic molecule, or upon certain substances present in the serum. After, however, insensitiveness to the action of the toxophorous group. these substances have disappeared, as they always do in It has been shown with regard to the former, for example, the course of time, the animal still possesses immunity that the nervous system of the fowl, which possesses (active) for a varying period. This apparently depends immunity against tetanus toxin, has little combining upon some alteration in the cells of the body, but its exact affinity for it. The non-sensitiveness of a cell to a toxic nature is not known. body when brought into immediate relationship cannot, The destruction of bacteria by direct cellular agency however, at present be explained. Then as regards both in natural and acquired immunity must not be over- natural powers of destroying bacteria, phagocytosis aided looked. The behaviour of certain cells, especi- by chemiotaxis plays a part, and it can be understood that cyfosls. ally leucocytes, in infective conditions led an animal whose phagocytes are attracted by a particular .Metchnikoff to place great importance on phago- bacterium will have an advantage over one in which this cytosis. In this process there are two factors con- action is absent. The natural bactericidal power of the cerned, viz., the ingestion of bacteria by the cells, and serum, as tested outside the body, also shows variations in the subsequent intracellular digestion. If either of different animals. Observations made on this property these is wanting or interfered with, phagocytosis will with respect to the anthrax bacillus at first gave the hope necessarily fail as a means of defence. As regards the that variations in natural immunity could be thus exformer, leucocytes are guided chiefly by chemiotaxis, i.e., by plained, but further investigation showed that immunity sensitiveness to chemical substances in their surroundings did not vary pari passu with this property. It is, more—a property which is not peculiar to them but is pos- over, doubtful whether the bactericidal power of the serum sessed by various unicellular organisms, including motile in the living body is always indicated by the results bacteria. When the cell moves from a less to a greater obtained in vitro. We therefore cannot fully explain in degree of concentration, i.e., towards the focus of produc- every case the exact property or process on which the tion, the chemiotaxis is termed positive; wThen the con- destruction of a bacterium in normal tissues depends. verse obtains, negative. This apparently purposive move- _ Authorities.—Bacteriological literature has become so extenment has been pointed out by Verworn to depend upon sive that it is impossible to give here references to original articles, stimulation to contraction or the reverse. MetchnikofF even the more important. A number of these, giving an account showed that in animals immune to a given organism of classical researches, were translated from French and German, and published by the New Sydenham Society under the title phagocytosis is present, whereas in susceptible animals it Micro-parasites in Disease : Selected Essays, in 1886. The followis deficient or absent. He also showed that the develop- ing list contains some of the more important books published ment of artificial immunity is attended by the appearance within recent yearsAbbott. Principles of Bacteriology, 5th of phagocytosis; also, when an anti-serum is injected edit. London, 1899.—Crookshank. Bacteriology and Infective (with bibliography), 4th edit. London, 1896.—Duclaux. into an animal, the phagocytes which formerly were Diseases Traite de microbiologie, vols. i. and ii. Paris, 1899.—Flugge. indifferent might move towards and destroy the bacteria. Die Mikroorganismen, 3rd edit. Leipzig, 1896.—Fischer. VorIn the light of all the facts, however, especially those lesungen iiber Baktcricn. Jena, 1897.—Guxther. Einfiihrung witli regard to anti-bacterial sera, the presence of phago- in das Studium der Bakteriologie, 4th edit. Leipzig, 1893.— Heim. Lehrbuch der bacteriologischen UntersucJmng und Diagnocytosis cannot be regarded as the essence of immunity, stik. Stuttgart, 1894.—Hewlett. Manual of Bacteriology. Lonbut_ rather the evidence of its existence. It is not don, 1898.— Hueppe. Principles of Bacteriology (translation). sufficient to state that the leucocytes are stimulated to London, 1899.—Kaxthack and Drysdale. Practical Bacterioactivity; it is necessary to explain how this is brought logy. London, 1895. — Klein. Micro-organisms and Disease, about. When positive chemiotaxis is brought into play 3rd edit. London, 1896.—Loffler. Vorlesungcn iiber die Entwickelung der Lehre von dcr Bactcrien. Leipzig, by an anti-serum, it is just as likely that it is indirectly geschichtliche 1887.—M‘Fareand. Text-book upon the Pathogenic Bacteria. through some change produced in the bacterium by the London, 1896.—Muir and Ritchie. Manual of Bacteriology anti-serum as by a direct stimulation of phagocytes. We (with bibliography), 2nd edit. Edin. and London, 1899.— think that the importance of phagocytosis as an ex- Sternberg.—Manual of Bacteriology (with full bibliography), 2nd edit. New York, 1896.—Thoinot et Masselin. Precis de planation of immunity by Metchnikoff and his school has Microbie, 3rd edit. Paris, 1896.—Wurtz. Precis de bacteriologie been considerably over-rated, but on the other hand that it clinique. Paris, 1895.-—Woodhead. Bacteria and their Products is one valuable means of destroying bacteria. Extra- (with bibliography). London, 1891. The bacteriology of the cellular destruction in the various conditions mentioned is, infective diseases (with bibliography) is fully given in the System Medicine, edited by Clifford Allbutt. London, 1896-1900. For however, also an established fact. Evidence has been of references consult Ccntralbl. fur Bakter. u. Parasitenk. Jena, a rought forward within recent years that the leucocytes “ General Register ” of which down to June 1899 (vols. i.-xxv.) has constitute an important source of the antagonistic sub- been published ; also Index Mcdicus. (r. m.) stances which appear in the serum. Much of such Bacup, a municipal borough (1882) in the Rossenevidence possesses considerable weight, and seeing that dale parliamentary division of Lancashire, England, on the these cells possess active digestive powers it is by no Irwell, 20 miles N. of Manchester by rail. A borough means improbable that substances with corresponding police force has been organized (1887), and a borough fire properties may be set free by them. To ascribe such brigade constituted out of its members. An Established powers to them exclusively is, however, not iusti- church has been rebuilt and a theatre erected, whilst in fiable. 1893 commodious public baths and a well-arranged recrea^ have thus endeavoured to state some of the chief tion ground were presented to the town by Mr J. H.