THE DEGREE OF INFECTION IN RELATION TO THE PARASITICIDAL ACTIVITY OF CHEMO- THERAPEUTIC COMPOUNDS

In conducting tests for the parasiticidal activity of chemical agents, the time of their administration in relation to the degree of infection may definitely influence the results. In general terms it may be expected that a smaller amount of a compound would prove parasiticidal when given immediately after infection than when given later and after the infection has become stronger and more advanced. But this is not necessarily true, in so far at least as the treatment of experimental syphilis and trypanosomia-sis are concerned, as we hope to show in this communication. This is a subject of considerable importance, not only in arrang-ing the technic of parasiticidal tests in chemotherapeutic research, but also in relation to the mechanism of chemical disinfection of the tissues as well as having an important bearing upon the dos-age of chemical agents in the prophylaxis and abortive treatment of certain diseases and notably of syphilis. In general terms it would appear that the degree of parasiticidal activity of a compound is in the nature of a curve in relation to the degree of infection. When given before or immediately after inoculation with a pathogenic organism, a slightly larger amount may be required for complete sterilization than when the infection has been given a slight start whereas larger amounts are again required when the infection has become well established. In other words, the parasiticidal activity of chemical agents would appear to be more marked in experimental syphilis and trypanoso-miasis when administered just as the infections become general