HOST-PARASITE SPECIFICITY IN THE GENUS GIARDIA 153 



in their stools. Perhaps changes in diet are responsible (Hegner, 

 1923). The problem is open to experimental study. 



/. Pathogenicity. The terms lambliasis, giardiasis, and flagellate 

 diarrhea have been applied to pathological conditions supposed to 

 be due to infections with giardias. It has never been satisfactorily 

 established that the giardias are actually responsible for the con- 

 ditions observed. Many physicians who have been unable to find 

 any other etiological agent present believe that Giardia is respon- 

 sible. Giardias do not penetrate the intestinal wall. They do, how- 

 ever, cling to the epithelial cells with their sucking discs. 

 Jassinowsky (1927) estimated that over 37,000,000 giardias were 

 present in the jejunum of a single rabbit, that is, over 1,000,000 

 per square centimeter of mucous membrane. Such large numbers 

 might bring about a diarrheic condition as the result of irritation 

 or, as Haughwout (1918) has suggested, of interference with the 

 functions of the glands. 



In recent years a large number of reports have been published 

 implicating giardias in the production of cholecystitis. Case re- 

 ports on this subject do not enable one to come to a definite con- 

 clusion. The reader is referred to current numbers of the Tropical 

 Diseases Bulletin for abstracts of work being published on the 

 subject. 



A fact that may have a bearing on the pathogenicity of Giardia 

 is the discovery of red blood cells inside of the body of giardias 

 by Knowles (1928). The presence of red blood cells in a parasitic 

 protozoon is usually accepted as evidence of pathogenicity. That 

 this is not true in the case of trichomonad flagellates has been 

 shown by the writer f Hegner, 1928c). How the red blood cells 

 were ingested by giardias is difficult to understand. 



