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Trypanosoma lewisi, etc. 
Nuttall (1908, p. 299) seriously doubts that any such development 
as described by Prowazek actually takes place. He inclines to the 
opinion that Prowazek was deceived by extraneous flagellates. 
Patton and Strickland (1908, p. 323) “are forced to the conclusion 
that Prowazek has described part of the life cycle of a natural flagellate ” 
and believe it has no connection with T. lewisi. They believe Prowazek 
has described in part a typical Crithidia natural to the louse. 
Professor Nuttall (1908, pp. 296—301), whom I should here like to 
thank for his never-failing kindness and help, has recently confirmed the 
identity of the carriers of rat trypanosomiasis, and I have at the same 
time dissected a large number of rat-lice and fleas, with a view to 
following up any developmental phases which might occur in these 
insects. 
The fleas were kindly identified for us by the Hon. N. C. Rothschild 
as Gtenophthalmus ( Typhlopsylla) agyrtes Heller, with one or two excep¬ 
tions hereafter named. The rats from which the insects were taken 
came from Cherryhinton, Cambs. 
Since Prowazek traced the supposed development of T. lewisi in lice 
taken from rats in Berlin and Rovigno we tried to obtain a similar 
material to that with which he worked by importing wild rats ( Mus 
decumanus ) from Berlin, so that we might study the lice and trace the 
supposed development therein of T. lewisi, in view of the fact that we 
had signally failed to confirm Prowazek’s results with material collected 
in this country. 
The Author s Observations and Methods. 
The insects (lice or fleas) were dissected in - 8°/ 0 NaCl solution under 
a Zeiss binocular dissecting microscope, care being taken not to injure 
the intestine, which was isolated and examined in a fresh condition. At 
times special parts of the gut were divided off, teased in a minute drop 
of the saline solution, then dried rapidly in the air, fixed in absolute 
alcohol for 15 minutes and stained in Giemsa’s stain. Coelomic fluid 
was obtained for examination by snipping off an appendage close to the 
body, whereupon a droplet of the fluid would exude from the wound. 
The dissections and observations made may be grouped as follows: 
(A) Lice were examined from rats apparently not infected with 
T. lewisi. (B) Many lice were examined from rats more or less heavily 
infected with T. lewisi and observations were made upon the ingested 
trypanosomes in the alimentary tracts of the lice. ( C ) A few lice 
taken from rats infected with T. lewisi were dissected after fasting 
