126 DISEASES DUE TO PROTOZOA 



HABITAT. 



Parasites occur in the blood, lymphatic glands, cerebrospinal fluid 

 and probably in the fluid of the serous cavities, which facts point to 

 the lymphatic system as being the most important habitat. 



It may be very difificult to find the parasites in the peripheral blood. 

 When present they may be more readily found during a febrile attack. 



T. gambiense has not yet been cultivated on artificial media, but 

 it can be readily communicated to monkeys, dogs, rats, guinea-pigs 

 and other animals. 



The rat trypanosome, T. lewisi, has been cultivated through many 

 generations. 



During adverse conditions, such as increasing scarcity of nutri- 

 ment, lowering of temperature, addition of chemical solutions and the 

 influx of sera from non-susceptible animals, the trypanosomes tend to 

 agglutinate, e.g., to congregate in bunches, with their extremities 

 (anterior) directed towards the centre. 



One bunch may contain loo individuals. The parasites mav 

 disperse again, apparently unaltered and uninjured. 



In cultures, trypanosomes may assume a spherical form and lose 

 their flagellum. 



The time required for the trypanosome to remain in the fly before 

 transmitting the infection is probably 20 — 47 days (Manson). 



CLASSIFICATION. 



(After Bruce, Lectures before Royal College of Physicians, 1915.) 

 Classification is based upon : — 

 (i) Morphology. 



(2) Pathogenic action of animals. ^ 



(3) Mode of development in tsetse flies. 

 Cultivation is of no assistance at present. 



Inoculation experiments and serum diagnosis are not helpful for 

 diagnosis on the field. 



(i) Morphology. 



In fresh films one ascertains the general appearance of the trvpano- 

 somes and the kind of movement. Some vibrate about one spot, 

 others hurl themselves about the field with great power and velocity. 



Stained specimens give more exact details as to length, breadth, 

 cell contents, nucleus, micronucleus, undulating membranes and 

 flagellum. 



(2) Pathogenic action on animals. 



The passage of a trypanosome through a series of animals of the 

 same species exalts their virulence towards that animal, e.g., the wild 

 strain of the nagana trypanosome which kills a rat in 20 — 30 days, but 



