224 SECTIONAL ADDRESSES. 
VII. Conclusion. 
We have considered but a few examples of the directions in which 
chemotherapeutic investigation has proved practically fruitful, including 
some in which it shows, at the moment, the most hopeful signs of progress. 
If one considers any one group of investigations by itself, one may easily 
feel, at the same time, elated by the practical success obtained, in the cure 
of some infection which, but a few years ago, seemed beyond the reach of 
treatment, and depressed by the disharmony between the results of experi- 
ment and the theoretical conceptions, hitherto available, of the nature of 
the chemotherapeutic process. Some of the most notable practical triumphs 
in this field have resulted, not from experimental investigations based 
on theory, but from an almost empirical trial, on human patients suffering 
from one type of infection, of a remedy which had experimentally shown 
promising results in infections of a different, and sometimes of a widely 
different, type. The partial success of tartar emetic in trypanosome infec-~ 
tions might have justified a hope that it would have some effect in kala-azar, 
but hardly a prediction of its really remarkable efficacy in that previously 
intractable form of infection. Still less would it have justified expectation 
of the brillant success of this same drug in infections by the Schistosoma 
or Bilharzia-worm, which but recently seemed almost beyond the hope of 
any kind of treatment. With such instances in mind, one might, but a 
year or two ago, have been tempted to suggest that the attempts at theore- 
tical investigation, of the intimate mechanism of the chemotherapeutic 
process, had contributed little to the practical achievements, and that a 
reasonably intelligent empiricism was still the safest guide. I do not think 
that the suggestion would even then have been defensible, and it would 
assuredly have been stultified by the results of the past few years. 
Patient, systematic exploration, by routes of which the initial sections 
were already mapped in the early days of chemotherapy, has in these recent 
years again led to results of major importance, both for practical thera- 
peutics and for the theoretical basis of future advance. That the original 
theoretical framework begins to show itself inadequate for the expanding 
fabric is good reason for its reconstruction ; but we may well beware of 
hasty and wholesale rejection, remembering that it served the early builders 
well. I think that it is especially encouraging to note that, though, in the 
action of almost every remedy which has proved its value in the specific 
cure of infection, there are features which cannot be interpreted by a strict 
application of Ehrlich’s distribution hypothesis, the discrepancies begin 
to show a new congruity among themselves. Repeatedly we find pheno- 
mena which point to the need of modifying the theoretical structure in 
the same direction. The conception of a remedy not killing the parasites 
immediately, but modifying their virulence, or lowering their resistance 
to the body’s natural defences; of a remedy not acting as such, but in virtue 
of the formation from it in the body of some directly toxic product, either 
by a modification of its structure or by its union with some tissue consti- 
tuent; of an affinity of the remedy for certain cells of the host’s body, 
leading to the formation of a depot from which, in long persistent, never 
dangerous concentration, the curative substance is slowly released ; all 
these conceptions present themselves, again and again, as necessary for our 
