MALARIA ORGANISM 1 49 



the Stomach wall. Here an individual trypanosome may 

 multiply eight or ten fold, till the cell is a mere envelope 

 containing a moving skein of trypanosomes. These then 

 break out into the stomach, and may invade other cells. 

 Some migrate to the rectum and hind gut, whence they are 

 expelled with the excrement. Rats are infected by lick- 

 ing the excrement of the flea while cleaning their fur. 

 Leishmania donovani is a rounded non-flagellate stage of 

 a flagellate parasite, and occurs in the lining cells of blood 

 vessels, causing splenomegaly or Kala azar in tropical and 

 sub-tropical countries. Many attempts have been made 

 to discover the intermediate host of this parasite. Many 

 possible carriers, especially fleas and bugs, have been in- 

 vestigated, but so far without success. L, tropica is the 

 cause of the skin lesions known as oriental sore, a widely 

 distributed disease in warmer countries. Ulcerating 

 wounds develop chiefly in exposed parts of the body, such 

 as hands, feet, and head. The parasites are carried by 

 sand flies. 



3. Plasmodium vivax, the organism of benign tertian 

 malaria, has already been dealt with (pp. 125 and 146). As 

 in most Haemosporidia, the schizogony phase of the life- 

 history is intracellular within a red blood cell, while the 

 spo'rogony phase is passed in a carrier insect. The two 

 species P. malaria and P. falciparum cause quartan 

 malaria and malignant tertian malaria respectively. The 

 life-history in each case is very similar to P. vivax. Plas- 

 modium prcecox (Proteosoma) , the parasite of bird malaria, 

 is transmitted by the mosquito, Culex fafigans, and an 

 allied parasite of the pigeon, Hcemoproteus columbce, by a 

 biting fly, Lynchia maura. 



In Piroplasma {Babesia) bovis the very characteristic 

 first part of the life-history is within the red blood cells of 

 cattle and other animals, the second part — not yet fully 

 understood — within a tick. This minute pear-shaped 

 parasite is the cause of Texas or Red-Water Fever, a 

 formidable cattle disease in certain parts of America and 

 in Australia. 



Among the other parasitic Sporozoa are various coccidia 

 (Eimeria), which are found in the intestine and related 

 parts of horses, pigs, sheep, and other mammals, of 



