Gr. H. F. Nutt all 
297 
Exp. I. Three fleas ( Ceratophyllus fasciatus) were removed from 
a wild rat (Mus decumanus ) which was infected with T. lewisi. The 
fleas were immediately placed upon a white rat whose blood had been 
previously examined at intervals with negative results for about a 
month. The rat remained isolated. Daily examination of the rat’s 
blood proved negative until the 7th day when T. lewisi was found. 
Exp. II. Four days after the trypanosomes had first been found 
in the blood of the rat in Experiment I, the animal was killed and one 
flea was recovered. This flea was placed on another tame rat, but in 
this case no infection followed. (Experiments I and II were carried out 
in March, 1908.) 
Exp. III. In this experiment 1 the tame rat upon which the fleas 
(Ctenopthalmus [ Typhlopsylla ] agyrtes [Heller]) 2 were placed was 
rigorously isolated in a flea-proof cage constructed after the pattern of 
those used by the Indian Plague Commission for their rat and flea 
experiments (see Journ. of Hygiene, 1906, Vol. vi. p. 435, Plate IV). The 
object of using this apparatus was to raise rat fleas in the laboratory. 
Eleven days (24. xi. to 4. xii. 1908) elapsed before trypanosomes appeared 
in the rat’s blood : 
Day 1. Blood examination of rat negative. Ten fleas were placed 
upon the rat, the fleas having been removed immediately before from a 
wild rat that was heavily infected with T. lewisi. 
Day 3. Blood examination negative. 
Day 4. Blood examination negative. Eight fleas were placed on 
the rat, the fleas having been removed immediately before from a wild 
rat which showed T. lewisi in its blood two days before it was killed and 
the fleas removed; no trypanosomes could be found microscopically on 
the day when the fleas were collected. 
Days 5—10. Blood examination negative. On the 10th day, one 
flea from a wild rat infected with trypanosomes was transferred directly 
to the tame rat. 
Day 11. Blood examination positive : 1 T. lewisi found in a fresh 
blood film. 
1 This experiment was carried out in conjunction with Messrs Patton and Strickland. 
2 Some of the fleas were kindly determined for me by the Hon. N. C. Rothschild, who 
states that Ctenopthalmus agyrtes has not apparently been found before on Mus decumanus. 
All the rats harbouring C. agyrtes were captured in one spot (Cherryhinton Brook, 
Cambridge). It is possible that one or two C. fasciatus may have been amongst the fleas 
put on this rat, since out of a batch of 18 fleas collected from rats from this locality one 
specimen belonged to this species. In Exp. IV the living fleas were determined by me 
before being placed on the white rat. 
19—2 
