1910.] 



Trypanosoma lewisi hy the Rat-Jlea. 



285 



Experiment D. 



Cage D colonised with 162 fleas that had been exposed to infection from 2 p.m. on 

 December 7 to noon on December 8, i.e. for a period of 22 hours only. 



Kat. 



Put in. 



Taken out. 



Jtvesuit. 



Trfpanosomes 

 first seen. 



Multiplication 

 ended. 



Dl 



December 



8 



December 



11 



0 







D2 





11 



3) 



13 



0 







D3 





14. 





15 



+ 



December 21 



Rat died 26/12/09 

















before multipli- 

















cation ended. 



D4 





16 



» 



17 



0 







D5 





18 





20 



0 







D6 



J) 



20 





22 



0 







D7 



»» 



22 





24 



0 







D8 



J) 



24 





28 



+ 



January 3 



January 8 



D9 



)) 



28 



January 



3 



+ 



„ 4 



10 



D 10 



January 



3 





6 



0 







Dll 





6 





10 



+ 



January 13 



January 19 



D12 



)) 



■ 



10 





13 



+ 



17 



„ ■ 23 



Experiment E. 



Cage E colonised with 50 fleas that had been exposed to infection from 2 p.m. on 



December 7 to noon on December 8, a period of 22 hours. (See account of 

 Experiment D.) 



Rat. 



Put in. 



Taken out. 



Result. 



Trypanosomes 

 first seen. 



Multiplication 

 ended. 



El 



December 8 

 „ 11 



December 11 

 left in 



0 

 + 



January 10 



January 15 



E2 





Remarks on Experiment E. — Allowing 12 days for the multiplication-period 

 in the rat, we arrive at January 3 as being the date on which Eat E 2 

 became infected. The length of the incubation-period in the flea would thus 

 appear to have been 26 or 27 days in this experiment, but this long incuba- 

 tion-period is, in our opinion, capable of a different explanation. We know 

 that fleas once infective retain infection, and as Eat E 2 was left in Cage E, 

 we may suppose that, being comparatively immune to begin with, it with- 

 stood infection for a long time, but that at last its resistance was overcome. 

 That some tame rats are resistant in this way is shown by the breaks in 

 Experiment D, and perhaps even more strikingly by the single break 

 (Eat C 14) in the series in Experiment C. 



EEFERENCES. 



Nuttall, G. H. F. (1908). "The Transmission of Trypanosoma lewisi by Fleas and Lice," 



'Parasitology,' vol. 1, pp. 296—301. 

 Bagshawe, A. G. (1909). Sleeping Sickness Bureau, Bulletin No. 10, pp. 370, 371. 



