Summary and Conclusions The experiments recorded above confirm and extend the results obtained by Roehl (1926) on the action of plasmochin on malaria in birds. Daily doses of 1.5 mgm. given orally are effective but are not easily tolerated by the birds. Heavy doses of 1.0 and 0.5 mgm. given daily for five succeeding days after a single inoculation prevent acute infections but do not prevent the appearance of parasites in the blood. Similarly smaller doses of from 0.07 to 0.2 mgm. given on five successive days after parasites appeared in the blood prevented acute infections but not the continuance of parasites in the blood. Daily small doses of plasmochin (0.1 mgm.) prevented the appearance of parasites in the blood of birds that were at the same time given daily inoculations of parasites. Plasmochin in doses of 0.1 mgm. for two weeks prevented the death of birds with acute infections that were deprived of large quantities of blood. The death of a bird suffering from a severe relapse was also apparently prevented by daily doses of 0.1 mgm. for two weeks. Plasmochin is thus shown to be a very effective therapeutic agent in bird malaria. It does not, however, destroy all the parasites in the body of the host and hence does not free the host from the possibility of relapse. On this account efforts should be continued to discover a drug that will destroy all of the parasites and hence prevent what is probably the greatest single factor in the spread of malaria,—relapse.