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ON THE NATURAL OCCURRENCE OF HERPETO- 
MONADS (LEPTOMONADS) IN MICE. 
By H. B. PANTHAM, M.A., D.Sc., 
Christ's College, Cambridge, and Liverjwol School of Tropical Medicine, 
AND ANNIE PORTER, D.Sc., F.L.S., 
Beit Memorial Research Fellow, Quick Laboratory, University of 
Cambridge. 
(With 7 Text-figures.) 
While engaged in experimental researches on the introduction of 
insect flagellates, belonging to the genera Herpetomonas and Crithidia, 
into vertebrates, we have recalled to mind some former observations 
of ours made in 1909. When examining the blood of mice artificially 
infected with the spirochaetes of relapsing fever in the Quick Laboratory, 
Cambridge, we observed flagellates in the peripheral blood of the mice. 
These flagellates, which were scanty, were studied in fresh preparations 
by us and drawings of the organism were made with the camera lucida. 
Some of these drawings are now reproduced, together with others made 
by us subsequently. The flagellates were also observed by Professor 
Nuttall and his laboratory assistant, Mr B. G. Clarke, and we were 
unanimously agreed that the flagellates belonged to the genus Her¬ 
petomonas, or Leptomonas as some have since preferred to call it. The 
significance of the presence of herpetomonads in the blood of mice was 
very puzzling at the time, and pressure of other work prevented the 
subject being followed up. During 1911 and 1912, these flagellate 
organisms have been seen by all of us, but they were always evanescent 
and could not be found in fixed and stained preparations. The parasites 
were seen on different occasions in three mice altogether. 
The Protozoon presented the typical aspect of a herpetomonad and 
was uniflagellate. The flagellar end was rounded and the body gradually 
