MALARIA 275 



The malarial organism has not been cultivated by any 

 artificial method yet devised. Undoubtedly the parasite 

 has a home outside the body, but we do not know for 

 certain what this is. It is not certain whether water may 

 not be in some cases a medium for the conveyance of the 

 disease. It is probable that the parasite passes through 

 a metamorphosis in the body or bodies of animals other 

 than man. But as yet little is known respecting the life- 

 history of this organism outside the human body, and 

 until we do but little can be done in the way of devising 

 scientific preventative measures. 



Forms of the Malarial Parasite. — From some external 

 source the organism finds its way into the blood, and here 

 it attacks the red blood corpuscles, each germ making its 

 way into a red blood corpuscle. On examining the 

 corpuscles, a certain proportion of them will be seen to 

 contain a pale, nebulous, ill-defined body, which at first 

 occupies but a small extent of the interior of the corpuscle 

 (Fig. 21 — 1). Soon this amceboid body grows in size, 

 becomes more defined, changes its shape, sometimes 

 assuming a ring-like form, and begins to develop black 

 pigment granules in its interior (Fig. 21 — 2). These pig- 

 1. 2. 3 4. 5. 



Fig. 21. — Evolution of the Malarial Organism (mtra-corpuscular 



bodies). 



ment granules exhibit slow movements. As the pigmented 

 body becomes larger the amceboid movements grow less, 

 while the pigment tends to concentrate (Fig. 21 — 3). This 

 pigment is no doubt derived from the haemoglobin of the 

 red corpuscles, the parasite growing at the expense of the 

 latter. 



18—2 



