MALARIA 371 



diseases are " cosmopolitan." Tuberculosis, for example, may occur 

 in all parts of the world ; so may pneumonia or typhoid. But the 

 five diseases named above are in a greater or lesser degree endennc in 

 tropical regions.* 



1. Malaria 



The term malaria (lit., bad air) is often applied rather to a 

 group of fevers than to one specific affection. Such fevers have 

 certain points in common. One common feature is that, with few 

 exceptions, the disease originates in the blood. A second feature is 

 the elaboration of a black or brown pigment from the haemoglobin 

 present in the blood corpuscles. And a third common character is 

 that these diseases are produced not by bacteria but by Ticematozoa, 

 that is to say, protozoa which can live and perform their functions 

 in the blood. The term " malaria " should, however, be reserved for 

 the specific disease caused by the malarial parasite. 



For many years the group of diseases represented by malaria 

 were designated miasmatic, owing to the belief that they were caused 

 by some damp and unhealthy condition of the soil, from which 

 emanated a miasm or soil ferment. Thus was explained their 

 prevalence on and around marshy tracts of land, and their prevention 

 by land drainage. Whilst these two latter features remain true, a 

 new interpretation has been placed upon them. 



In 1880 Laveran first discovered and described parasites in 

 the blood cells of malarial patients, and on further investigation 

 it was soon found that these assumed many different forms. 

 These differences depend upon the kind of fever and the stage of 

 fever. 



The reasons for believing that Laveran's bodies though they 

 have not yet been cultivated outside the human body are the 

 specific cause of malaria are briefly these : (1) The parasites found 

 in the blood of malarial patients of all countries are the same. (2) 

 Such parasites are not found in healthy persons. (3) Their develop- 

 ment fully accounts for the production of the melanoemia and 

 malarial pigmentations of viscera owing to the melanin-forming 

 property of the parasite. (4) The phases in the development of 

 such parasites corresponds with the clinical course of malaria (Golgi). 

 (5) Quinine, which cures malaria, kills the parasite. (6) Malaria 

 can be conveyed by the introduction of this parasite into the blood 



* The term endemic indicates that a disease affects people within a certain 

 geographical limit, and which seems therefore to arise from local or particular 

 causes. Epidemic indicates that a disease attacks a large number of people at the 

 same time and approximately in the same place. Whereas a pandemic is the same 

 with an indefinitely wide distribution. 



