24 TROPICAL MEDICINE AND HYGIENE 



extensive amoeboid movements, and containing finely 

 divided black pigment (fig. 8, a, b). 



More advanced stages are very rarely seen in the peri- 

 pheral blood, but parasites with the pigment aggregated 

 in a dense black block, and even sporulating, are occa- 

 sionally found. Sometimes, usually just before death, such 

 forms may even be numerous (fig. 8, c, d, e). In these 

 cases the red cells containing the more advanced para- 

 sites are often found in clumps ; they agglutinate because 

 of their stickiness. These advanced forms are abundant 

 in the capillaries in the internal organs and appear to 

 be accidental only in the peripheral circulation. The 

 change induced by the parasite in the red cells is such 

 that these become sticky and adhere to each other and 

 to the walls of the blood-vessels, especially in the capil- 

 laries in the internal organs where the current is slow and 

 uniform. 



In addition to the young forms of the parasites, game- 

 tocytes are also found in the peripheral blood. These 

 are not present in the early stages of the fever, and are 

 rarely numerous when there is pyrexia, and young forms 

 are abundant ; they are more common after the pyrexia 

 has disappeared, and when no young forms can be found, 

 and are therefore numerous during convalescence from 

 a febrile attack. 



The gametocytes of subtertian malaria are of a special 

 shape and quite different from the sporocytes of sub- 

 tertian or the gametocytes of the other forms of malaria. 

 They are sausage-shaped bodies, longer than the diameter 

 of a red corpuscle, and the ends are free from pigment ; 

 this is aggregated into a clump near the centre (fig. 8, x). 

 In the freshly shed blood they are still enclosed in a red 

 corpuscle, but this is almost colourless and stretched 

 out by the parasite. Gametocytes in all species develop 

 from some of the " ring " forms. Why this form 

 develops instead of asexual sporulating forms is uncertain. 

 Possibly the formation of some antibodies renders the 

 conditions of life less favourable for the parasite, and then 



