150 PROTOZOAN PARASITISM 



that this is an indication of pathogenicity. Hogue 

 (1928) has grown Trichomonas in tissue cultures of 

 epithelium, fibroblasts and sympathetic nerve fibers 

 without apparent injury to these cells. 



The work of Hadley (1916), who thought the 

 tissue invading parasite of turkeys in the disease 

 Blackhead was a Trichomonas, has not been sup- 

 ported. 



Experimental infection, such as recorded by the 

 writer (1915), has not shown the production of dis- 

 ease in a convincing way. Such experiments are 

 subject to a variety of error. 



The occasional observation of a red blood corpus- 

 cle ingesting trichomonad cannot be held to indi- 

 cate any pathogenic role according to Hegner (1928), 

 who induced eight species of Trichomonas from as 

 many different animals to ingest red blood corpuscles 

 from seven different species of animals, in culture 

 tube. 



An experiment of the writer in which Trichomonas 

 hominis, as well as Blastocystis, was cultivated in a 

 medium composed of one part of the host's own blood 

 serum to nine parts of 0.9% sodium chloride solution, 

 suggests that there are no inhibitory or destructive 

 antibodies produced by the host and, therefore, proba- 

 bly no toxic absorption. 



The condition which most often calls attention to 

 its presence and in which it is most often suspected 

 of an etiologic role is diarrhoea, with frequent watery 

 stools of no peculiar gross or microscopic character. 



