480 MALARIAL FEVEK. 



5. Flagellated Organisms. If a drop of blood be ex- 

 amined under the microscope for some time, flagellated organ- 

 isms may be found. So far as is known, they do not occur as 

 such in the circulating blood, but only appear in the blood 

 outside the body. They are derived from the crescents 

 or from the larger pigmented intracorpuscular bodies. In 

 the former case, when watched under the microscope the 

 crescents alter their shape, becoming straight, then oval, 

 and ultimately spherical. The pigment granules first become 

 arranged as a ring, and afterwards show a peculiar vibratory 

 movement, which is apparently produced by flagella which 

 have formed within the sphere. When this stage is reached, 

 the flagella, usually three or four, though sometimes more, 

 are shot through the envelope, sometimes simultaneously, 

 sometimes one after the other, and present a very rapid 

 lashing action. The flagella are very delicate filaments, with 

 sometimes a slight bulbous swelling at their free extremity 

 (Fig. 107). They may afterwards become detached, and 

 move away with an active independent movement. In the 

 case of their development from the large intracorpuscular 

 bodies, the pigment shows an agitated movement in the 

 same way, and ultimately the flagella are suddenly shot out. 



There has been, and still is, great diversity of opinion 

 concerning the nature of the crescentic and the flagellated 

 bodies. The view which appears to be best supported is, 

 that the former represent a sort of resting form for the life 

 of the organisms outside the body, the first stage of which 

 is the flagellated condition. This view has been advanced 

 notably by Manson, who considers that the flagella are 

 really flagellated spores which undergo further change, and 

 that this probably occurs in the body of mosquitoes which 

 have taken up blood containing the parasite. Ross supports 

 this view, and has found that in the body of the mosquito 

 many of the crescents become spherical, and develop into 

 the flagellated forms. Hitherto it has not been found 

 possible to infect healthy individuals by allowing them to be 

 bitten by mosquitoes containing the parasites. Possibly, as 

 Manson suggests, the latter undergo further change, and are 



