E. Hindle 159 
produced a pathogenic variety, for which it is convenient to retain the specific 
name R. quintana. 
An interesting parallel may be observed in the case of parasitic flagellates. 
It is well known that these occur in the alimentary canal of a large variety 
of invertebrates and some species such as Trypanosoma and Leishmania have 
become adapted to living in the blood of vertebrates. Most of these flagellates 
inhabit the alimentary canal of blood-sucking insects, but, as in the case, of 
Rickettsia , some are found in animals that never feed on blood and therefore 
cannot acquire the infection in this way. On the other hand the results of 
Laveran and Franchini (1914) and Fantham and Porter (1916) have shown 
that it is possible to infect vertebrates artificially by the inoculation of 
flagellates from various species of invertebrates, and there is no reason to 
suppose that the introduction of parasites into the body by natural methods 
would be any less successful. 
In conclusion, I should like to express heartiest thanks to my friend Prof. 
G. H. F. Nuttall, F.R.S., for his continual assistance and helpful advice. 
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