xic bodies in such a fluid, and Brieger and Fraenkel (1890) found
that they were proteids, to which they gave the name "toxalbumins." Though
subsequent researches have on the whole confirmed these results, it is
still a matter of dispute whether these proteids are the true toxins or
merely contain the toxic bodies precipitated along with them. In the United
Kingdom the work of Sidney Martin, in the separation of toxic substances
from the bodies of those who have died from certain diseases, is also
worthy of mention. Immunity against toxins also became a subject of
investigation, and the result was the discovery of the antitoxic action of
the serum of animals immunized against tetanus toxin by E. Behring and
Kitazato (1890), and by Tizzoni and Cattani. A similar result was also
obtained in the case of diphtheria. The facts with regard to passive
immunity were thus established and were put to practical application by the
introduction of diphtheria antitoxin as a therapeutic agent in 1894. The
technique of serum preparation has become since that time greatly
elaborated and improved, the work of P. Ehrlich in this respect being
specially noteworthy. The laws of passive immunity were shown to hold also
in the case of immunity against living organisms by R. Pfeiffer (1894), and
various anti-bacterial sera have been introduced. Of these the
anti-streptococcic serum of A. Marmorek (1895) is one of the best known.
The principles of protective inoculation have been developed and
practically applied on a large scale, notably by W. M. W. Haffkine in the
case of cholera (1893) and plague (1896), and more recently by Wright and
Semple in the case of typhoid fever. One other discovery of great
importance may be mentioned, viz. the agglutinative action of the serum of
a patient suffering from a bacterial disease, first described in the case
of typhoid fever independently by Widal and by Gruenbaum in 1896, though
led up to by the work of Pfeiffer, Gruber and Durham and others. Thus a new
aid was added to medical science, viz. serum diagnosis of disease. The last
decade of the 19th century will stand out in the history of medical science
as the period in which serum therapeutics and serum diagnosis had their
birth.

In recent years the relations of toxin and antitoxin, still obscure, have
been the subject of much study and controversy. It was formerly supposed
that the injection of attenuated cultures or dead organisms--vaccines in
the wi