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DIAGNOSIS AND PATHOLOGICAL ANATOMY. 481
fever, in pyaemia, puerperal fever, erysipelas, osteomyelitis,
and many other diseases, microscopical organisms resem­
bling fungi of different kinds were found in the blood and
in certain secretions or tissues, the idea inevitably suggested
itself of ascribing the origin and cause of such diseases to
these bodies.
The scientific proof that these lowly organized forms do
actually stand in a causal relation to particular diseases
was only possible after these organisms had been success-
fe :. fully isolated by special methods of research, inoculated on
healthy animals and found to produce the diseases in
question. These demands have, up to the present, only
•*• been satisfied in splenic fever, relapsing fever, malignant
erysipelas, diphtheria, and Asiatic cholera. But a multitude
of facts and probabilities point to pathogenic bacteria
being the active cause of the origin and spread of tuber­
culosis, leprosy, typhus and enteric fevers, scarlet fever,
septicaemia, malarious and many other forms of disease.
The difficulties encountered in carrying on these
inquiries experimentally, especially in the choice of an
animal suitable for inoculation and susceptible to the
diseases, render it evident that results can only be arrived
at slowly. The facts hitherto established have given a
firmer basis to setiology, inasmuch as they have rendered
manifest the really active causes of the diseases and have
consequently indicated both to pathology and to thera­
peutics the paths upon which, for the future, they must
travel.
Materia medica has during the latter decades changed
from a study of pharmaceutical wares into a science of
pharmacodynamics which, being in close association with
physiology and experimental pathology, is supported by
clinical experience and experiments on living animals. By
means of it a bridge may here and there be thrown across
the deep chasm which divides the theory and the practice
of medicine.
During the same period the pharmacopoeia has been
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