878 IMMUNOLOGY 



thorities such as Wenyon (1926) believe that many of the species for- 

 merly recognized as distinct should be combined (cf. Becker, Chapter 

 XVII). 



The work on piroplasms, although lacking in conclusiveness, has at 

 least served to direct the attention of systematists to the problems of 

 classification (Theiler, 1912; Stockman and Wragg, 1914; du Toit, 

 1919; Brumpt, 1920). 



In malaria cross-immunity tests have been extensively employed 

 (Manwell, 1938), whereas in amoebiasis complement fixation tests 

 have occasionally been used (Menendez, 1932). 



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 Alda Calleja, M. de. 1936. Estado actual de los estudios sobre sueroflocula- 



cion en el paludismo. Med. Paises Calidos, 9: 203-36. 

 Aschoff, L. 1924. Das reticulo-endotheliale system. Ergebn. inn. Med. Kin- 



derheilk., 26: 1-118. 

 Barber, M. A. 1936. The time required for the examination of thick blood 



films in malaria studies, and the use of polychromatophilia as an index 



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 Ben Harel, S. 1923. Studies of bird malaria in relation to the mechanism of re- 

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 Bloom, W. 1938. Lymphocytes and monocytes: theories of hematopoiesis. 



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penhyg., 22: 49-55. 

 Boyd, G. H. 1929a. Induced variations in the asexual cycle of Plasmodium 



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1929b. Experimental modification of the reproductive activity of Plas- 

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