THE HAEMOFLAGELLATES 



207 



fluid; they have also been seen, in post-mortem examination, in the 

 lateral ventricles of the brain. It is this invasion by the parasites of 

 the nervous system that marks the transition of the case from one of 

 " Trypanosoma-kvei " (while the parasites are confined to the blood) to 

 one of sleeping-sickness. The results of the change are soon apparent 

 in the onset of lassitude, tremor, and the other associated nervous 

 /symptoms which characterise this dreadful malady. 



Death from trypanosomosis is due either to weakness and emaciation 

 (in chronic cases), or to blocking of the cerebral capillaries by the parasites 

 (where these are abundant and the disease consequently acute and rapid), 

 or to the disorganisation of the nervous system (paraplegic and sleeping- 

 sickness forms). Laveran and Mesnil have expressed the opinion that 

 some factor in addition to the presence of the parasites themselves 

 especially when these are rare is requisite to explain the severe effects 

 produced, and suggest that the Trypanosomes secrete a toxine. Neither 

 they nor other investigators have, so far, been able to discover traces of 

 any such substance. In post-mortem examination, the most obvious 

 pathological feature is hypertrophy of the spleen, which may be very 

 pronounced. The lymphatic glands in the neck, inguinal region, etc., 

 are often greatly swollen and contain numerous parasites. 



The spleen and lymphatic glands are undoubtedly the organs 

 which react most strongly 



to the parasites, and their /^' : ^ V:;; $%L_ ---""A 

 enlarged condition is, prob- 

 ably, to a great extent 

 due to enhanced activity 

 in elaborating blood -cor- c -. 

 puscles and leucocytes to 

 cope with the enemy. In- 

 gestion and dissolution of 

 the Trypanosomes by 

 phagocytes has frequently 

 been observed (Fig. 6). 

 It is very likely also that 

 the haematopoetic organs 

 secrete some chemical or 



physiological Substance Phagocytosis of 2 - Uwi *L In A the leucocyte is 



which exerts a harm'ful beginning to engulf the Trypanosome ; in 13 the latter 



,. ,. ., is completely intracellular ; C-E show the gradual dis- 



actlOn On the parasites, solution of the parasite Q>). , nucleus of leucocyte ; 



paii<sin<y fVi^m fn nrnrJortrr* c ' ingested blood - corpuscles ; v, vacuoles remaining 



Causing tnem tO Undergo after their dissolution. (After Lav. and Mesn.) 



involution and assume 



weird-looking "amoeboid" and "plasmodial" forms. 



3. COMPARATIVE MORPHOLOGY. 



Trypanosomes vary greatly with regard to size ; even in one 

 and the same species this variation is often noticeable, especially 



