introduced into Vertebrates Al 
| 
I 
i 
| Bere 
contains flagellates in various stages of division and the resistant, 
post-flagellate forms—a fact not without significance in our 
|experiments. 
III. Laxperimental work. 
By a series of experiments we have established that Herpeto- 
-monas jaculum, normally parasitic in the Hemipteran, Nepa 
“cinerea, can become pathogenic to mice when fed to them or when 
they are inoculated with it. We have also determined the form of 
the flagellate mostly responsible for the production of the disease 
| and most capable of development within the body of the vertebrate. 
The blood of the experimental mice and of the control mice 
“was very carefully examined before they were used and no protozoa 
were found therein. Examination of the rodents’ faeces, both 
before and during the progress of the experiments, was entirely 
negative. Some experiments were performed in Liverpool with 
mice and Nepa obtained locally, and others were carried out in 
-Cambridge, the Nepa being collected from small ponds on Coe 
Fen. As the results obtained in each place were identical, the 
influence of climatic conditions and of possible variations in the 
strain of H. jaculwm used were eliminated. As the mice used 
were mostly young, they and their controls were kept at or near body 
temperature. 
| In most cases an interval of a few hours was sufficient to allow 
of the appearance of rounded, non-flagellate forms of H. jaculum 
_in the peripheral blood. The mice became weaker and either died 
or were killed in extremis. Examination of their organs showed 
the presence of non-flagellate (leishmaniform) and of flagellate 
forms in the liver, spleen, bone-marrow and blood, occasionally in 
other organs. ‘The liver was always the seat of heaviest infection. 
The parasites kept the facies of H. jaculwm and were pathogenic 
to the mice. The number of flagellate forms present and their 
fine development (see Pl. 1) was noteworthy, and is unlike what 
has been obtained before in the experiments by Laveran and 
_ Franchini with other insect flagellates in mice. 
Much time was devoted to the examination of the parasites in 
freshly drawn blood and in emulsions of organs taken at death. 
Smears of the organs were also fixed wet with Bouin’s fluid or 
with osmic vapour followed by absolute alcohol. For staining, 
_ Giemsa’s solution, haematoxylin and iron-haematoxylin, with or 
without eosin, were employed. 
| Experiment 1 (A.P.). Young, wild mouse, ? , weight 3°3 grams, 
was fed once on teased anterior portions (oesophagus and stomach) 
of the alimentary tract of Nepa cinerea, infected with Herpeto- 
 monas jaculum, and was afterwards fed only on milk. The infected 
