520 MALARIAL FEVER. 



of development. They appear in the blood after the fever 

 has lasted for some time, apparently remain unchanged 

 through the attacks of pyrexia, and may persist for a con- 

 siderable period after the fever has gone, being often 

 present in the cachexia or anaemia following these fevers. 



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

 amined under the microscope for some time, flagellated 

 organisms 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 either from 

 the crescents or from the larger pigmented intra-corpuscular 

 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 enve- 

 lope, 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. 124). They may 

 afterwards become detached, and move away with an active 

 independent movement. In the case of their development 

 from the large intra-corpuscular 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 



