35 2 
' Transmission .—Infection has been effected by 
means of a rat flea (P. fasciatus ) and, it is stated, by the 
rat louse (H aematofiinus sfinulosus ) also. With the 
louse we have experimented, but always in vain. 
Prowazek, who, however, also failed to transmit 
infection by the louse, describes a complex develop¬ 
mental cycle in the gut of the louse. 
(i) Fertilisation of a female (thick form, with 
spherical nucleus) by a male trypanosome (slender, with 
a slender nucleus) occurs. (2) Formation of an 
ookinet with a single spherical nucleus. (3) Develop¬ 
ment of a trypanosome from this ; as the flagellum now 
Fig. 109 . F. lewisi: shewing rosette formation as the result of division 
appears at the same end as the blepharoplast, this is 
taken to be the anterior end of the trypanosome ; later, 
the blepharoplast moves away to the opposite (pos¬ 
terior) end, viz., that of its normal position. Besides 
this cycle, the trypanosomes are also said to assume 
gregarine-like non-flagellate forms, which penetrate 
between the epithelial cells. How far these forms 
belong to P. lewisi and how far to possible natural 
trypanosomes of the louse’s gut, remains to be seen. 
Cultivation .—-(Novy and MacNeal). Mix agar, 
melted and cooled W50 0 C., with defibrinated rabbit’s 
