464 J. R. BRADFORD AND H. G. PLIMMEH. 



VI [. The Difpeeences between the Trypanosoma Brucii 

 AND the Trypanosoma pound in Sewer Rats. 



The distribution of the Trypanosoma Lewisi amongst 

 sewer rats seems to be very variable^ the organism being 

 prevalent in some districts and not in others. For instance, 

 we first examined six sewer rats from the south of London 

 with negative results; then twelve from the north of London, 

 of which number five contained the Trypanosoma Lewisi; 

 then twenty-four from the south of London again with nega- 

 tive results. 



There are the following points of difference between the 

 sewer rat Trypanosoma and that found in Nagana. The 

 former, the Trypanosoma Lewisi, are a little shorter and 

 somewhat thinner than the Trypanosoma Brucii, and the 

 posterior end is much inore pointed, as is shown in fig. 46. 

 The micronucleus is placed transversely as a rule, and is 

 larger. The macronucleus is placed at the end of the body 

 of the organism, instead of in the middle, as in the Trypano- 

 soma Brucii. The protoplasm of the Trypanosoma Lewisi 

 is not so homogeneous as that of the Nagana Trypanosoma. 

 We have not observed any such forms as we have described 

 as conjugations, nor any amoeboid nor plasmodial forms in 

 the blood of the sewei' rat ; apparently in this organism 

 multiplication by longitudinal division only seems to be the 

 rule. If the Trypanosoma Lewisi be examined in the 

 living blood under critical illumination, three dark spots can 

 be seen in nearly all the organisms, apart from the nuclear 

 structures; one is very near the micronucleus, and the other 

 two between this and the macronucleus, on that side of the 

 body opposite the undulating membi'ane. These are not visible 

 in the stained specimens. The Trypanosoma Lewisi does 

 not protect the animal containing it in the smallest degree 

 from the Trypanosoma Brucii ; sewer rats naturally 

 infected Avith the former were inoculated with the latter, and 

 died in the usual time. 



