immunity against bacterial disease.

[Sidenote: Historical summary.]

The demonstration by Pasteur that definite diseases could be produced by
bacteria, proved a great stimulus to research in the etiology of infective
conditions, and the result was a rapid advance in human knowledge. An
all-important factor in this remarkable progress was the introduction by
Koch of solid culture media, of the "plate-method," &c., an account of
which he published in 1881. By means of these the modes of cultivation, and
especially of separation, of bacteria were greatly simplified. Various
modifications have since been made, but the routine methods in
bacteriological procedure still employed are in great part those given by
Koch. 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. Thus the organisms of suppuration, tubercle, glanders,
diphtheria, typhoid fever, cholera, tetanus, and others were identified,
and their relationship to the individual diseases established. In the last
decade of the 19th century the chief discoveries were of the bacillus of
influenza (1892), of the bacillus of plague (1894) and of the bacillus of
dysentery (1898). Immunity against diseases caused by bacteria has been the
subject of systematic research from 1880 onwards. In producing active
immunity by the attenuated virus, Duguid and J. S. Burdon-Sanderson and
W. S. Greenfield in Great Britain, and Pasteur, Toussaint and Chauveau in
France, were pioneers. The work of Metchnikoff, dating from about 1884, has
proved of high importance, his theory of phagocytosis (_vide infra_) having
given a great stimulus to research, and having also contributed to
important advances. The modes by which bacteria produce their effects also
became a subject of study, and attention was naturally turned to their
toxic products. The earlier work, notably that of L. Brieger, chiefly
concerned ptomaines (_vide infra_), but no great advance resulted. 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. Roux and A.
Yersin (1888), and in the case of tetanus a little later by various
observers. Research was thus directed towards ascertaining the nature of
the to