THE HiEMOrLAGELLATES. 295 



and, correlated with this, the kinetonucleus is situated fartlier from the 

 anterior end than it is in the more stumpy forms. Investigators are, liow- 

 ever, at one in considering that these differences are due merely to the 

 different habitat, since both varieties, when inoculated into other animals, 

 give rise to the same kind of form. The cerebro-spinal fluid would appear 

 to be less favourable a medium than the blood. T. gambiense is the 

 cause of human trypanosomosis in West and Central Africa, the earlier 

 stages of which, when the parasites are confined to the blood, are known as 

 Trypanosoma-fever, the later ones, after they have penetrated into the 

 cerebro-spinal canal,' constituting the deadly malady of sleeping sickness. 



Fig. 48. — T. gambiense, from the blood, (a, after Bruce and 

 Nabarro ; B, after Castellani.) 



It seems most probable that the original Vertebrate source or " reservoir " 

 of this parasite is some indigenous tribe or race of natives in whose blood — 

 and in all probability only in their blood — the Trypanosomes live, as it were, 

 normally, parasite and host having become mutually tolerant." Whether 

 any animal other than man is also a natural host, is quite unknown. If 



^ Plimmer (85) has lately expressed the view that the forms met with 

 in Trypanosoma-fever and sleeping-sickness are distinct species, basing 

 his opinion on the behaviour and appearance of the parasites after being 

 inoculated into the same host (rat), and also on the symptoms presented by 

 the latter in the two cases. The weight of evidence at present, however, is 

 decidedly against this view; see the Reports of the S. S. Comm., also 

 Brumpt and Wurtz (13), Laveran (38), Thomas and Linton (116), and 

 several other workers. 



* For various factors which have helped to bring unaccustomed, un- 

 adapted tribes and individuals into the zone of the parasite and have thus 

 led to the spread of the infection and its invasion of fresh regions in the 

 character of a fatal disease, the reader is referred to Lankester's instructive 

 article (31). 



