l8o THE PROTOZOA. 



posteriorly. There is a nucleus (macronucleus) and a blepharoplast 

 (micronucleus centrosome), the latter being located anteriorly as a 

 chromatin staining dot or rod. From this blepharoplast the flagellum 

 proceeds posteriorily bordering the undulating membrane and pro- 

 jecting freely beyond the posterior end. The nucleus is larger, 

 nearer the posterior end, and does not stain so intensely as the 

 blepharoplast. 



T. gambiense. This is the trypanosome causing human trypano- 

 somiasis, the latter stage of which is known as sleeping sickness. It is 

 from 17 to 28/1 long, and from 1.5 to 2/z wide. 



It is very difficult to distinguish the human trypanosome from some 

 of the other pathogenic ones by staining methods. The immunity 

 test is the most reliable. An animal recovered from an infection by a 

 certain trypanosome does not possess immunity for other pathogenic 

 ones. Novy and McNeal cultivated T. lewisi in water of condensation 

 on blood agar, but up to the present T. gambiense has not been culti- 

 vated. It is present in the blood, usually in exceedingly small numbers, 

 and in the lymphatic glands of patients. It is by puncture of the 

 glands that we have the best means of finding the parasites. It is also 

 found in the cerebrospinal fluid in sleeping sickness. The parasite 

 stains readily with Wright's stain. The transmitting agent is the 

 Glossina palpalis. It is not known whether this occurs by direct or 

 indirect transmission. At any rate, there must be some peculiarity 

 about the tsetse fly, either in the reaction of its salivary secretion or 

 otherwise, to make it the only well-recognized agent in the spread of 

 the disease. No tsetse fly, no trypanosomiasis. Koch observed 

 certain developmental forms in the bulb of the proboscis, but whether 

 they represented a developmental cycle or not is not settled. 



Other authorities think it possible that trypanosomes may encyst in 

 the digestive tract and so the flies transmit the disease along with their 

 faeces. This does not seem to be possible in connection with human 

 infections. Koch found several cases where infection had taken place 

 by coitus. This is the method of infection in T. equiperdum, a 

 trypanosome disease of horses. 



Of the more important trypanosome diseases of animals may be 

 mentioned : 



