The results described above indicate that quinanil and the compound 2 (p-dimethylaminoanil)-β-naphthoquinoline methochloride might be successfully used as selective reagents for the isolation of insect flagellates of the genus Leptomonas.
The actual concentrations, which might be successfully used in the culture media, will show some variation according to whether the flagellate is adapted, at the time, to luxuriant growth in the media used. For example, in preliminary experiments, the Leptomonas from Polietes and Calliphora grew better in Locke serum agar than in bouillon, and quinanil was more toxic in the latter than in the former. In the present experiments the reverse held, but in later ones, not here recorded, where the flagellates have again grown more abundantly in Locke serum agar, growth regularly occurs in 1/6000 concentrations of quinanil in this medium. There is little doubt from other results, not yet published, that some Leptomonas forms can be made to show modification of cultural requirements through adaptation. It is probable therefore that in the attempted isolation of fresh forms from the gut of the insect, several kinds of media might have to be employed.
After this work was completed, in several attempts made to purify laboratory-contaminated cultures, success was attained by following the suggested methods, using quinanil and 2 (p-dimethylaminoanil)-β-naphthoquinoline methochloride. The compound 113 was even less toxic to the Leptomonas forms in media than was the compound 52, but its bactericidal action was correspondingly weaker. The few experiments conducted in the absence of media indicated that this substance might have proved very useful, but unfortunately the material gave out and further supplies were not available. In the preliminary treatment of gut contents, acriflavine, owing to its apparently bacteriostatic action, might prove of some value for destroying organisms of the Bacillus prodigiosus type.
Consideration of the results obtained with gentian violet, brilliant green, and the two anilquinolines, 2 (p-dimethylaminoanil)-6-acetylaminoquinoline methochloride and methosulphate, suggests that these compounds are of no use as selective bactericidal substances permitting the growth of Leptomonas forms. The combined action of two or more of these substances has not yet been studied.
As our results indicate, little success is to be hoped for in this direction with the Leishmania forms, which are extremely susceptible to the toxic effects of all the substances employed. Two points of interest were obtained from these results. It might be noted that Leptomonas ctenocephali reacted in a similar manner to the Leishmania forms but that Leishmania tropica (“Baghdad”) behaved like a Leptomonas form. This strain appeared similar in all respects to the other Leishmania forms, but it was the only one readily acclimatised to media containing no blood. Its morphology also showed some modification after a time.
We are greatly indebted to Dr St John-Brooks, Curator of the National Collection of Type Cultures, and to Prof. S. Adler of the Hebrew University, Jerusalem, for certain of the cultures of Leishmania and Leptomonas used, and also to Dr K. E. Cooper for the gift of the anilquinoline derivatives and for much helpful advice.
One of us (F. C. H.) has also been in receipt of grants from the Medical Research Council, and he would like to take this opportunity of expressing his thanks to that body.
