92 THE ANIMAL PARASITES OF MAN 



infect a rat. Minchin and Thomson formerly considered that the 

 small, stumpy, infective trypanosomes pass forwards from the rectum 

 into the stomach, and " appear to be regurgitated into the rat's blood 

 when the flea feeds." However, the small infective trypanosomes 

 were previously described by Svvellengrebel and Strickland. 1 They 

 may be found in the flea's faeces. Noller (igi2) 2 has found that the 

 development of T. lewisi proceeds quite well in the dog flea (Cteno- 

 cephalns can-is) in Germany. Wenyon confirms this, and states that 

 the human flea, Pulex irritans, and the Indian rat-flea, Xenopsylhi 

 cheopis, are also able to serve as true hosts for 7\ lewisi. 



Noller stated that rats were not infected with T. lewisi by infective 

 fleas biting them, but by the rats licking up the faeces passed by the 



^ FIG. y^. Trypanosonia lewisi. Developmental stages from rectum of rat-flea. A, early 

 rectal form; C, D, division of crithidial form; E, group of crithidial forms; F I, crithidial 

 forms without free flagella, some becoming rounded ; J M, transitional forms to tiypanosome 

 type seen in N, which represents the final foim in the flea, x 2,000. (After Minchin.) 



fleas while feeding. This is not in agreement with Minchin and 

 Thomson's earlier views of regurgitation, which, apparently, they 

 have now abandoned. 3 Wenyon (1912) confirms Keller's experi- 

 ments. He took a dog flea, containing infective trypanosomes in 

 its faeces, and allowed it to feed on a clean rat. The faeces of the 

 flea, passed while feeding, were carefully "collected on a cover glass 

 and taken up in culture fluid with a fine glass pipette." The contents 

 of the pipette were discharged into the mouth of a second clean rat. 

 Injury to the rat's mouth was carefully avoided. The first rat, on 

 which the infective flea was fed, did not become infected, while the 



1 Parasttology, iii, p. 360. 2 Arch. f. Frotistenkunde, xxv, p. 386. 



3 Report to Advis. Comm. Trop. Dis. Research Fund for 1913, p. 7^. 



