Abstract
Chemotherapy is essentially the study of the toxic and therapeutic properties of chemical compounds. Its main purpose is to establish the maximum tolerated and minimum curative doses. The numerical value representing the ratio of these two doses is the chemotherapeutic index. Chemical compounds possessing the highest chemotherapeutic indices in experimental infection are usually the best adapted for the treatment of disease in man.
Ehrlich, Bertheim and Hata 2 were the first to engage in systematic chemotherapeutic work, in the course of which numerous new chemical bodies were synthesized. They were all derivatives of one certain compound called atoxyl, selected because it was the only organic arsenical known at that time which possessed trypanocidal properties, although to a very small degree. The changes in the chemical constitution of atoxyl led finally to the elaboration of a derivative many times more powerful in the cure of protozoön infection. At present, a considerable amount of work is being performed along the lines established by Ehrlich and numerous organic arsenicals have been prepared, still, the synthesis of new chemical compounds merely for the purpose of testing their toxic and therapeutic properties and thereby finding the best drug for the treatment of disease will not advance the science of chemotherapy beyond mere empiricism.
Is it impossible to find a relationship between certain atomic groupings and toxicity or curative effect? Once the influence of these various groups upon the parasite or the animal body is appraised the synthesis of new compounds will assume a more rational course. Some very valuable findings have already been made in this direction by Ehrlich who discovered the remarkable trypanocidal and spirillocidal effects of the arseno group (As = As) when attached to the nuclear carbon atom.
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