TRYPANOSOMA LEWISI 473 



crithidia forms, till the whole of the rectum may be covered with organisms. 

 All these forms appear in the faeces of the fleas, but it is probable that 

 it is only the small trypanosomes which bring about infection. Though 

 the main development and attachment takes place in the rectum, this 

 may also occur, but to a smaller extent, at the anterior end of the hind- 

 gut near the pyloric opening. 



Though Swellengrebel and Strickland (1910) had established the fact 

 that rats could not be infected by the bites of the flea, the exact mechanism 

 of infection was not understood till Noller {I9l2d) published the results 

 of his experiments. This observer employed the convenient method of 

 handling individual fleas by tethering them on fine wire, a jirocedure 

 adopted by showmen. By its use the movements of a flea can be com- 

 pletely controlled. Noller's results were confirmed by the writer (19136), 

 using the wire method, and later by Minchin and Thompson (1915) with 

 untethered fleas. Noller found that the fleas repeatedly passed faeces or 

 blood during the act of feeding, and that this could be collected and 

 examined. About six days after the flea had fed on an infected rat, the 

 small infective trypanosomes, as well as other forms, appeared in its 

 faeces. Fleas in this condition were allowed to feed on uninfected rats, 

 care being taken to prevent the voided faeces contaminating the skin. 

 The faeces ejected were received on a cover-glass held behind the flea while 

 feeding, and were transferred at once to the mouth of another rat. This 

 experiment, repeated many times, always resulted in infection of the 

 second rat and never the one bitten. Observing rats on which free fleas 

 were placed, it was noted that the latter had the habit of congregating 

 about the root of the tail, where they would feed when the rat was asleep. 

 Aroused by their bites, the rat turns its head to allay the irritation or 

 dislodge the fleas, which, startled by its movements, eject their faeces and 

 escape into the fur. The freshly-passed faeces are then easily licked up 

 by the rat. In this manner, by fleas passing from infected to uninfected 

 rats, T. lewisi is transmitted in nature. Minchin and Thompson, working 

 with Ceratojphyllus fasciatus in the free condition on rats, noted that only 

 a small percentage actually became infected. In the case of the fleas 

 used by the writer, all became infected after feeding on an infected rat. 

 Yamasaki (1924) obtained similar results. 



This mode of transmission was demonstrated by Noller (1912(^) in the 

 case of the dog flea, Ctenocephalus canis, and by the writer (19136) for this 

 flea, as well as the human flea, Pulex irritans, and the Indian plague flea, 

 Xenopsylla chcBopis. Minchin and Thompson (1915) proved it for the 

 European rat flea, Ceratophyllus fasciatus, so that it is clear that many 

 species of flea may act as vectors of T. leivisi. Furthermore, the complete 

 development may take place in fleas which in nature rarely, if ever, have 



