Researches on Insect Flagellates introduced into Vertebrates. 139 
“next day a slight swelling appeared at the site of inoculation. 
This soon disappeared. The blood examination was negative, as 
“it was on subsequent days. Six days after inoculation, the fish 
died. Smears of the tissue near the site of moculation contained 
contracting parasites approaching a non-flagellate condition, and 
also flagellate forms. Elongate and flagellate herpetomonads 
were present in the heart blood, while leishmaniform and elon- 
gating parasites were present in the liver and spleen. The control 
fish died a day after the experimental one, but no herpetomonad 
in any stage of development was found in its organs. 
Experiment 2 (H.B.F.). A male stickleback was fed with the 
gut of a Nepa cinerea containing a few flagellate forms of Herpeto- 
monas jaculum. It only lived two days, and no parasites were 
found at autopsy. 
(b) Haperiments with Amphibia. 
Experiment 3 (A.P.). A large male frog, Rana temporaria, was 
inoculated intraperitoneally with the gut contents of three Gerris 
paludum, which contained flagellate and a few postflagellate forms 
of Crithidia gerridis. Two days after inoculation, some oval and 
elongating parasites were found in the blood. Subsequent examina- 
tions were negative. The frog became thinner and died on the 
evening of the 29th day after the experiment began. Smears of 
the organs showed that the liver contained a number of the oval, 
encysted, postflagellate forms of the protozoon, as well as fully 
developed flagellates presenting the typical crithidial facies. Elon- 
gating forms, transitional between the non-flagellate and full 
flagellate forms, occurred both free and in mononuclear cells in 
the liver. A few cells contained two rounded or elongating 
Crithidia. 
It may be mentioned that here, as in all our experiments in 
which Crithidia gerridis was used, no transition to a trypanosome 
was ever seen. 
Eaperiment 4 (H.B.F.). A male frog, Rana temporaria, was 
inoculated intraperitoneally with the fore-gut of a Nepa cinerea, 
containing preflagellate and young flagellate forms of Herpeto- 
monas jaculum. No exudate appeared at the site of inoculation. 
On the 4th day after the commencement of the experiment, 
a leishmaniform parasite was found in an endothelial cell. 
Blood smears were negative from then to the 10th day, when 
leishmaniform stages were found in the blood. Certain of these 
forms showed a thin cyst wall, and certainly represented the 
postflagellate form as produced at the end of the developmental 
cycle in the insect host. Further blood examinations were nega- 
tive until the 31st day, when both leishmaniform and elongating 
herpetomonads were present. Subsequent blood examinations 
10—2 
