studied and is commonly taken as the type. It is non-pathogenic 

 and is transmitted from one animal to another through the bite of 

 the rat-flea {Ceratophyllus fasciatus) or dog-flea {Ctenocephalus 

 canis). 



The most important human trypanosome disease is sleeping 

 sickness, distributed through equatorial Africa from Uganda west- 

 wards. The organism, T. gambiense, is transmitted through the 

 bite of a tsetse fly, Glossina palpalis. The incubation period lasts 

 from ten days to three weeks, and the disease may be carried for 

 some months. It is characterized by nervous changes, producing 

 muscular fatigue and torpor, especially marked during the day. 



A similar disease affecting African domesticated animals, and 

 carried in the blood of native animals is known as nagana. It is 

 transmitted through the bite of another species of tsetse fly, G. 

 morsitans, the direct causative agent being T. brucei. The carrier, 

 G. morsitans, has also been shown to be capable or transmitting 

 both T. gambiense and T. rhodesiense, the causative organism 

 of the "Rhodesian" type of sleeping sickness. Dourine, a try- 

 panosome disease of horses, the causative agent of which is T. 

 equiperdum, is significant because of its presence in Western 

 Canada, following introduction into North America in imported 

 Percheron stock. 



The herpetomonads form a composite group consisting of 

 elongated cells with parabasal body and terminal free fiagellum 

 (Herpetomonas), similar cells with a free undulating membrane 

 attached to the flagellum (Crithidia), and simple cells without 

 fiagellum or membrane, occurring as intracellular parasites, but 

 having flagellated phases as in Herpetomonas. The cell forms are 

 significant for their resemblances to the trypanosome and ordinary 

 flagellate (Euglena) forms. Herpetomonas and Crithidia are 

 intestinal parasites of arthropods. The intracellular form, known 

 as Leishmania, includes L. donovani, the organism of Indian 

 kala-azar, and L. tropica, the organism of Delhi boil. 



In kala-azar the parasites are found inside the endothelial cells 

 of the capillaries, for the most part, of visceral organs. The para- 

 sitic cell (Leishman-Donovan body) is rounded or oval in shape, 

 and contains two chromatin bodies, of which one, much smaller 

 than the other, is a parabasal body. When grown on a culture 

 medium the organism assumes a flagellated form like Herpetomonas, 

 indicating that the intracellular form is an adaptively fixed or 

 "resting" stage. 



Delhi boil is a cutaneous disease contributed chiefly in India 

 and the Orient, but also more or less generally in the tropics. The 

 boils occur commonly about the face. The parasite is found in the 



