362 
Trypan osoma lewisi 
2. Material and Methods. 
The fleas used for the study of the supposed life-cycle were hatched 
out from larvae preserved in a flea-breeding apparatus. This culture 
existed since 24th November, 1908. The fleas were fed on uninfected 
rats. The lice were directly taken from the rats because it is impossible 
to keep them alive without constantly feeding them on a rat. For the 
study of the living flagellate the intestines (of flea or louse) were taken 
out, without rupturing them, and were put between a slide and cover- 
slip. Sometimes such preparations were kept for 24 hours in an 
incubator at 28° C.; but the death of the parasites prevented generally 
a more prolonged observation. In order to make stained preparations, 
different parts of the gut (of flea or louse) were teased in a drop of 
0'6°/ 0 salt solution and smeared out. The preparations were then put 
in absolute alcohol before they were dried completely and stained with 
Giemsa’s solution. To produce a satisfactory staining it was generally 
necessary to stain for 12 hours. Beside this method other preparations 
were fixed, without drying, in corrosive alcohol and subsequently stained 
with Heidenhain’s iron hematoxylin (Breinl’s modification). Both methods 
gave satisfactory results which did not differ at all from one another. 
We found the old method of fixing and staining a very good one, not 
deserving the severe criticisms to which it has been subjected of late 
(cf. Swellengrebel, 1910). 
3. The development of T. lewisi in the rat flea 
(Geratophyllus fasciatus ). 
To study this point 83 fleas out of the uninfected laboratory culture 
were allowed to feed for 12 hours on an infected rat, which had been 
infected ten days before and showed trypanosomes in the last stage of 
the period of division. After feeding they Avere taken off and preserved 
in a gauze bag at 13—16° C., Avhere they were allowed to feed each 
third day on a non-infected rat. Each day for 18 days 4—6 (some¬ 
times more) fleas were dissected and preparations were made of the 
contents of the different parts of the gut (midgut, hindgut, rectum). 
The following table (I) shows the rate of infection for each daj r . 
We see that 44‘6°/o of these fleas showed stages of development and 
even when excluding the first two days (during which the morphological 
alteration was a very slight one) the rate of iufectiou was still 36'9°/ 0 . 
