The study here reported had for its object the investigation of the effects of quinine and plasmochin on infections with Plasmodium circumflexum, and comparison of the results with those already obtained by similar treatment of infections with the other four species of avian malaria (Plasmodium capistrani excepted). A total of fifty-five female canaries were used in the treated series. The results may be summarized as follows:
1.Basing the list which is given below partly on the data reported in the present paper and partly on data previously reported, the susceptibility of the five species of avian plasmodia here considered to treatment with quinine and plasmochin appears to be as follows, the most susceptible being given first:
1. Plasmodium rouxi
1. Plasmodium elongatum
2. Plasmodium praecox
3. Plasmodium cathemerium
2. Plasmodium praecox
4. Plasmodium circumfiexum
3. Plasmodium circumfiexum
5. Plasmodium elongatum
4. Plasmodium cathemerium
It should be noted that in the first list (quinine) the differences between Praecox, cathemerium and circumflexum are very small, and that this is also true of praecox and circumflexum in the second list. Elongatum and rouxi are placed at the top of the second list, and rouxi heads the first list, chiefly because infections with this species could be readily sterilized with the drug in question. Cathemerium and circumflexum occupy the positions they do (even though plasmochin is effective in removing parasites from the peripheral blood in a relatively short time) largely for the contrary reason; in other cases the percentage of parasite-free days was the chief factor governing the place of the species in the scale.
2.As with the other species, Plasmodium circumflexum is more amenable to plasmochin than to quinine. When sterilization is not brought about relapse within a month generally occurs, but does so less frequently than in praecox infections, and may be deferred for two months or even longer. This is correlated with the fact that the parasite-level in chronic infections of circumflexum is generally established at a much lower level than in the case of praecox, and is to be compared in this respect only to cathemerium.
3.Plasmochin in combination with quinine is apparently no better than when used separately, and may even be less satisfactory—due possibly to quinine intoxication.
4.As with the other species, treatment during the incubation period is much more effective than when postponed until parasites appear. A considerable proportion of cases may be completely aborted in the former case, as demonstrated by continued freedom from relapse and by subinoculation, with subsequent reinfection, but so far no case in which parasites had already appeared has been sterilized.
5.There is little evidence that gametocytes are either more or less susceptible to plasmochin and quinine than the asexual stages.
6.Study of the rates of reproduction of the different species, and other peculiarities of the life-cycle, suggests that the degree of susceptibility to drug therapy may depend in large part on these factors—particularly in the case of plasmochin.