I FLAGELLATA 51 



Three species of Leishmania have been clearly recognized so far : — 

 (i) L. donovani, the parasite of Kala-azar. This species has been 



found to occur in Dogs and possibly this animal is the normal host of the 



parasite. 



(2) L. infantum, which produces an enlargement of the spleen, 

 something like that of Kala-azar, in children in Algiers, Tunis and South 

 Italy. 



(3) L. tropica, which is found in superficial sores in the skin (Tropical 

 Ulcer, Delhi Boil). As these occur always on exposed parts of the body 

 transmission may in this case be effected by some flying insect. L. tropica 

 occurs in Northern Africa and Asia, and appears also to be responsible for 

 an ulcerative disease prevalent in some districts of Paraguay and Brazil 

 and often mistaken for Syphilis or Yaws. 



The Flagellata are Protozoa of usually comparatively small size and 

 possessing in the normal adult phase of their life-history one or more 

 flagella by the movements of which they swim. They show a remarkable 

 variety in their form, while of even greater interest is the variety in their 

 mode of nutrition. In attempts to draw a boundary between the animal 

 and the vegetable kingdom a principal factor made use of is the difference 

 in mode of nutrition — an animal typically nourishing itself by the 

 ingestion of complex organic food material (holozoic nutrition) while a 

 plant either builds up its complex organic material out of simpler 

 components as in the case of green plants (holophytic nutrition) or else 

 absorbs products of metabolism or decay by its general surface (saprophytic 

 nutrition). The invalidity of any such general distinction is at once 

 clear from the study of the Flagellata, for here we have an assemblage 

 of creatures undoubtedly closely related together and yet making use 

 of all three types of nutrition. 



The great majority of flagellates live free lives in water but many 

 members of the group have taken on a parasitic mode of existence. 

 They are particularly common in the alimentary canal of various animals. 

 Insects such as flies are very prone to harbour them {Crithidia, Lepto- 

 monas, etc.) and it seems probable that such forms as Trypanosomas 

 are to be regarded as primitively insect parasites which with the develop- 

 ment of the blood-sucking habit have spread to vertebrates. 



III. SPOROZOA 



We will commence the study of the Sporozoa by going over in some 

 detail the life -history of two illustrative genera — Monocystis, chosen 



