74 
Insect Flagellates , 
Summarising the results of Laveran and his collaborators, and Fantbam 
and Porter, Laveran (1917) states that the experiments firmly establish the 
affinity between Herpetomonas (and Crithidia), on the one hand, and Leishmania 
on the other, an affinity which, from the phylogenetic point of view, is well 
recognised. Fantham (1915, 1915 a) goes a step further in his conclusions: he 
asserts that the experiments conducted by him and Porter, and Laveran and 
Franchini, prove that Leishmaniases are arthropod-borne herpetomoniases, 
and that these maladies have evolved mainly from insect flagellates. The 
experiments on artificial infection of vertebrates with these flagellates, 
according to this author, actually represent ‘'leishmaniasis in the making.'' 
Most of the flagellates with which Laveran and his collaborators dealt, 
and some with which Fantham and Porter worked, belong to insects which 
in nature are closely associated with some mammal, and it is known that some 
of these insects are capable of transmitting the haemo-flagellates to other 
vertebrate hosts, and infecting them, whilst others ( e.g . the sand-fly) may 
eventually prove to be such intermediate hosts. On this account it is not 
surprising to find that the flagellates which parasitise the gut, and which may 
after all be insect stages of vertebrate haemo-flagellates, can produce infection 
when introduced into other vertebrates. In such cases no special adaptability 
is required. 
Notwithstanding these facts, similar experiments repeated by other 
investigators produced negative results. Thus Chatton (1919) and Noller (1920) 
repeated some of Laveran and Franchini’s (1919) experiments with H. cteno- 
cephali, but failed to find any traces of infection; similar experiments were 
made by Wenyon (1914) with the same flagellate, also with negative results. 
The last-named author also failed to produce any infection in rats inoculated 
with the flagellates of Tabanus socius (Wenyon, 1908). 
As regards the pathogenicity of flagellates from insects which are not 
naturally associated with any vertebrate, this question is of more complex 
character. If such insect flagellates may become pathogenic to vertebrates 
when artificially introduced into them, we must assume that their power of 
adaptation is extraordinary, both as regards the time required for such 
adaptation in one generation, and as regards adaptation to the change of 
environment. This is the more surprising, if we take into account such protozoa 
as free-living amoebae which are frequently taken in by man and other animals, 
and pass through the whole digestive tract of the animal without becoming 
adapted to life in the latter, whereas closely allied forms of amoebae are found 
as obligatory parasites in the intestine of the same animal (cf. Wenyon, 1915; 
Dobell, 1919). 
I shall now proceed with a description of my own experiments, and will 
return to the discussion of these questions later. 
For my experiments I used the following flagellates: Herpetomonas jaculum 
from the water-scorpion (Nepa cinerea), H. calliphorae from the blue-bottle 
