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Herpetomonas jaculum (Leger) 
1. Effects of Light. 
The movements of the Herpetomonads were slowed in proportion 
as the intensity of ordinary white light was decreased. Green light 
also caused the organism to move more slowly. 
2. Effect of Temperature. 
In tap-water at 15° C. the organisms moved rapidly; at 18° C. their 
movements were more active, although the rise in temperature was 
slight. 
3. Effects of Various Media. 
(i) Tap-water. The parasites behaved as in the gut of the host 
and lived for several hours. 
(ii) 0'75°/o NaCl. The flagellates died more rapidly in this liquid 
than in tap-water. 
(iii) Glycerine. The movements of Herpetomonads were slowed 
by dilute glycerine. 
(iv) 1 % acetic acid killed the flagellates, which appeared to swell 
slowly and then burst. 
(v) 1 °/o caustic potash killed the parasites rapidly. Their bodies 
dissolved vei'y slowly. 
(vi) A medium composed of the gut contents of other Nepa , 
recently fed on larvae of Chironomus, caused starved Herpetomonads 
placed therein to develop granules in their cytoplasm. 
(vii) Human blood derived from a pricked finger, likewise fish 
and amphibian blood, when mixed with the parasites, had the effect of 
causing growth, rapid longitudinal division and increase of granules in 
the protoplasm of the Herpetomonads. 
(viii) A medium composed of crushed Cidex larvae in water, when 
mixed with H. jaculum, caused the flagellates to divide, but the division 
was not so frequent nor so rapid as recorded uuder (vii). 
Experiments (vii) and (viii) suggest that division of the flagellate 
Herpetomonad takes place rapidly under natural conditions, after 
ingestion of blood by the host. 
General Remarks. 
Herpetomonas jaculum (Leger) is a parasite whose complete life is 
passed within the alimentary tract of JS'epa cinerea. Its long body, 
blunt flagellated end and single flagellum, in addition to the three 
phases of its existence, place the parasite in the genus Herpetomonas 
as originally constituted. Saville Kent (1881) created the genus 
