I.—PHYSIOLOGY. 22) 
; the toxic and curative actions of the arsenical derivatives, and that a 
formation by the trypanosome of the sulphydrile compound, in excess of 
_ its vital need, may be the basis of acquired resistance. If certain dyes 
similarly affect this cellular oxidation system, the production under their 
influence of strains of trypanosomes resistant to arsenic would also be 
explained. So stated the suggestion leaves many aspects of the problem 
still unconsidered; but it may at least be allowed the merit of an attempt 
to interpret the action of these drugs in terms of known biochemical facts. 
IV. Emetine and Dysentery. 
) To turn to another example of a chemotherapeutic problem, I may 
_ mention briefly some results obtained, some years ago, by Mr. Clifford 
- Dobell and myself, in an attempt to explore the curative action of emetine 
and the other alkaloids of ipecacuanha in ameebic dysentery, with a view 
_ to finding a more effective treatment. At the time when we took up the 
| problem it seemed simple. Rogers had recorded that the amcebe obtained 
from a case of amcebic dysentery, and treated in vitro with emetine, were 
_ rapidly killed by the alkaloid in dilutions as high as one part in 100,000. 
This seemed to explain the action of emetine as a simple and direct one on 
the parasites, and to provide a rapid method for testing a series of com- 
pounds for their therapeutic possibilities. We failed, however, as other 
_ observers before and since have done, to confirm the observation ; on the 
_ contrary, we found that the dysenteric amcebse, obtained from cats 
secondarily infected, or, in a control observation, directly from man, were 
surprisingly insusceptible to the action of emetine, living for hours in 
concentrations much greater than the highest which they would tolerate 
_ of other alkaloids, which had no curative action in dysentery. One of 
_ the other natural alkaloids of ipecacuanha, methyl-psychotrine, and certain 
artificial derivatives of emetine, were much more effective in killing the 
_ amoebee in the test tube, and at the same time were practically devoid of 
_ the characteristic toxicity of emetine and cepheline for mammals and for 
man. Here, on the classical assumption of chemotherapy, should have 
_ been ideal remedies for amcebic infection—substances much more parasi- 
totropic and much less organotropic than those already known to be effec- 
tive. Yet each of them in turn, when administered to patients suffering 
_ from ameebic dysentery, in doses much larger than those in which emetine 
_ could be tolerated, produced no effect whatever on the dysentery, which 
promptly cleared up when emetine was subsequently given. Among the 
_ members of this group of alkaloids which were tried, the curative effect 
seemed to be proportional rather to their toxic and nauseating action on 
the patient, than to their lethal action on the isolated amcebe. Yet 
_ emetine and cephzline are not mere symptomatic remedies ; they definitely 
_ stop the progress of infection by the amcebe, and, properly administered, 
eliminate them altogether from the body. 
Yet another puzzling observation, made by Dobeil and myself, was 
_ that an ameebic infection which readily yielded to treatment with emetine 
in man, was entirely uninfluenced by emetine when transferred to the cat. 
_ Inno way is it possible to account for these facts without admitting a co- 
operation of the patient’s tissues in the curative action; nor, with that 
admission, can we do more than consider possibilities. We only know that 
