212 SECTIONAL ADDRESSES. 
and scientific efforts have produced. Modern Chemistry, indeed, has 
separated the alkaloids from these drugs, and has made it possible to 
identify among them the actively therapeutic constituents ; Protozoology 
has revealed the nature of the infections. We know now that cinchona owes 
its curative action chiefly to quinine and quinidine, and that they act as 
specific exterminators of the malaria parasites, and not simply as remedies 
for fevers in general; and we know that ipecacuanha owes its action to 
emetine and cepheline, and that these act as exterminators of the enta- 
mceba causing tropical dysentery, and not simply as symptomatic remedies 
for dysenteries of any kind. But chemistry has produced no better remedy 
for malaria than quinine, or for ameebic dysentery than emetine; and 
the method by which either of these alkaloids cuts short the infection by 
a particular parasite, the nature of its specific action, remains a fascinating 
problem. 
The modern development of chemotherapy, as a new department in 
therapeutic science, claiming the co-operation of parasitologists, micro- 
biologists, and synthetic chemists, did not take origin, however, simply 
from the study of these traditional remedies. It may be regarded rather as 
anoutcome of the study of the naturalantibodies. The investigation of these 
natural antagonists to infection produced a new therapeutic ideal. Not 
only had they shown themselves to have an intensely specific affinity for 
the infecting organism of the toxin which caused their production ; they 
were also perfectly harmless to the patient, behaving, in relation to his 
organism, as normal constituents of his body fluids and tissues. Ehrlich 
aptly compared them to magic bullets, constrained by a charm to fly 
straight to their specific objective, and to turn aside from anything else 
in their path. 
Of the artificial remedies, on the other hand, which man had empirically 
discovered, even of drugs like those just mentioned as being specific for 
certain infections, the best that could be hoped was that they would 
eliminate the parasite before they poisoned the patient* And thus, when 
the limitations of natural immunity were becoming clearer; when it was 
realised that to certain forms of infection, several of which had proved to be 
infections by protozoa, the body was unable to produce antibodies of 
sufficient potency to eliminate the infection and leave the patient immune; 
the question arose whether, with the new and growing powers afforded by 
synthetic chemistry, man could not so far rival Nature’s achievements as 
to produce, in the laboratory, substances specifically adapted to unite with 
and kill the protoplasm of these parasites, as the natural antibodies united 
with that of others, and to leave the tissues of the patient similarly un- 
affected. The ideal of this new and systematic Chemotherapy, as the 
imaginative genius of Paul Ehrlich conceived it, was to be the production 
by synthesis of substances with a powerful specific affinity for, and a 
consequent toxic action on, the protoplasm of the parasites, and none for 
that of the host—of substances, to use Ehrlich’s own terminology, which 
should be maximally parasitotropic and minimally organotropic. 
I want to invite your attention to-day to the results which, during the 
last twenty years, have been produced under the stimulus of this bold 
conception ; not, indeed, to attempt a survey or summary of all that has 
been done, but, in the light of a few of the suggestive facts which have 
emerged, to consider how far this hypothesis has justified itself, and whether 
