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-faveT " (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 

 enlarged condition is, prob- 

 ably, to a great extent 

 due to enhanced activity 

 in elaborating blood -cor- 

 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 

 eecrete some chemical or 

 physiological substance 

 which exerts a harmful 

 action on the parasites, 

 causing them to undergo 

 involution and assume 

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



In A the leucocyte is 



Fie. 6. 



Phagocytosis of T. lewisi. 



beginning to engulf the Trypanosome ; in B the latter 

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

 solution of the parasite (p). n, nucleus of leucocyte ; 

 c, ingested blood - corpuscles ; v, vacuoles remaining 

 after their dissolution. (After Lav. and Mesn.) 



3. COMPARATIVE MORPHOLOGY. 



Trypanosomes vary greatly with regard to size ; even in one 

 and the same species this variation is often noticeable, especially 



